Notes on Cereals. 17

Transcription

1 Notes on Cereals. 17 on though we no longer consist of the same material particles, and in tbe same way tbe chromosome may retain its individuality tbougb it basat one time been fed by cbromatin from the nucleokis, and at another time given up its chromatin to the nucleolus. It is quite true tbat " le dernier mot n'est pas encore dit sur la question de l'beredite, la question de la reduction, de l'essence des divisions sexuelles, ni meme sur la nature de la cinese somatique," ' but still I think we may say of the most recent view which is in essentials common to tbe Louvain and Bonn schools, " Se non fe vero, e bene trovato." ' F. A. Jansscns. " La spermatogonfcsc chez les Tritons." La Cellule, T. XIX NOTES ON CEREALS. BY ERIC DRABBLE. Through tbe kindness of Messrs. Gartons, Ltd., of Warrington, I have recently bad the opportunity of examining very fully their methods of producing new breeds of Cereals on their e.xperimental farm at Acton Grange, in Cheshire. A full account of their methods and results will be published elsewbere, but several points of general botanical interest bave been noticed in the course of the work, and a sbort account of tbese is given below. METHODS EMPLOYED IN PRODUCINO NEW BREEDS. Wbeat, Oats and Barley bave all been used experimentally. Races already possessing desirable qualities, in many cases combined witb less desirable or even undesirable characters bave been chosen as parents. Crosses bave been made by removing tbe anthers of the female parent at an early stage, and applying to tbe stigma pollen from tbe male parent. It is necessai-y to remove the stamens at a very early stage indeed, as it appears that the cereals are normally self-pollinated before tbe pales open. It is certain tbat the unopened flower sbows tbe presence of pollen upon its stigmatic lobes. When tbe stamens protrude tbey appear at first sight to be entire, but careful examination shows tbat a partial dehiscence lias already taken place, and tbrougb this tbe pollen grains found on the stigma bave come. Hence it is evident tbat the stamens must be removed carefully before sucb debiscence has taken place. Tbe pales are opened with forceps, the stamens removed, pollen from

2 18 Eric Drabble. the male parent is applied to the stigma, and the pales are again closed. The process of events in the flower previously to, and during pollination, is as follows. Before self-pollination has occurred the stigmas converge. The anthers then partially dehisce, and pollen is shed on to the stigmas while still enclosed within the pales. Immediately after this pollination the stigmas diverge and emerge laterally from between the pales. Now it is that cross-pollination may take place, though according to Mr. Garton's results, crossfertilization would appear to supervene but rarely. A few hours after the emergence of the stigmas they again converge, and this is accompanied by a general contraction of the stigmatic lobes. The evidence for self-pollination is strong, though this does not necessarily involve the absence of later cross-pollination, which may indeed be prepotent, but in no case has Mr. Garton been able to produce a hybrid by application of pollen from a male parent to the extruded stigma of the female the pollen must be applied to the stigma before it extrudes. The fruits of the flowers thus cross-pollinated are allowed to ripen, and are gathered and kept separately. They are sown next season, and all the grain from each plant is kept separately. This is sown in rows the following season, the produce of each plant having a row to itself. The resulting plants are found to show great sporting; some being superior in certain characters to the parents, others being Inferior. The plants which in the characters desired are found to be the best are noted, and the grain is kept and sown the following season. Again the resulting plants will show a tendency to sport, but lest markedly so than in the last season. The best are again selected and the grains sown, and a further selection is made, until finally a progeny is obtained in which the sporting is slight and almost negligible. The race is then said to be fixed. By this is meant that so long as the plants are allowed to breed naturally, as Mr. Garton believes entirely by self-fertilization, no further sporting will occur. COMPOSITE CROSSES. Many races may be combined in the production of new breeds. As an example may be cited the ancestry of the breed " New Era." The wheat known as "Talavera" was crossed with a form of Triticum spelta, and the progeny which we may call a was raised. At the same time the wheat "Bartweigen" was crossed with "Fultz," and again the progeny was raised ( 3). a was then crossed with /3 and

3 Notes on Cereals. repeated selecfiion of tbe most desirable forms resulted in the establishment of the new race "New Era." It may sometimes be desired to introduee into a hybrid characters possessed by two forms which will not readily cross, or which will not produce fertile offspring. In such a case each form is crossed with some other form for which it has "affinity," as the breeders express it, and the resulting offspring are then mated. This will in many cases lead to a progeny, some members of which possess the desired characters. Or suppose again that four varieties are crossed in pairs; the progeny of each is fixed and a cross between them is instituted, and suppose that some of the offspring show characters which it is desired to fix at once, altbougli the progeny as a whole is sporting, and will continue to sport for several generations. The desirable plants are each crossed back with one of the parents. In this way a fixation of the required characters in some of the progeny takes place quickly. This is of considerable interest and can be co-ordinated with certain facts of cytology. The members of the fixed type may deteriorate after several generations although they do not change their characters. Crosspollination amongst themselves will bring them back to their former vigour without causing undue sporting. A slight tendency to sporting may be induced, but not sufficient to materially change the race. It is of very great interest, however, to note that if the forms crossed have been grown under different conditions, although their ancestry has been the same, the sporting induced is greater than if they had been grown under exactly similar conditions. ig SOME RESULTS OF COMPOSITE CROSSING. A great defect of all cultivated wheats with the exception of T. turgidnin and T. spelta is that the grain tends to drop out when ripe. A serious drawback to these two forms of wheat, however, is tbat the rachis breaks up, so that on threshing, the spikelets are separated, each attached to a portion of the rachis. By crossing any of the cultivated forms of T. sativnm with a spelt wheat, varieties may be fixed which retain the grain but are without tbe property of breaking up. A breed has been produced which will retain its grain for four weeks. This is of great importance for large grain-growing countries where the whole of the crop must be harvested within the period between ripening and shedding of the grain. In Australia, where the grain is harvested by the stripper

4 2O Eric Drabble. which threshes the wheat in the process of harvesting, such breeds are useless. One of the peculiarities often shown by the products of composite crosses is that the spikelets instead of producing the normal number of grains about six become elongated and carry as many as fourteen grains. In certain cases the whole head becomes vegetative and the pales grow out as foliage leaves^ four inches or more in length. BARLEY. In the Barleys on each side of the rachis are rows of spikelets. These spikelets are in sets of three, a central one, and two lateral ones. In the two-rowed barleys only the central spikelet of each triplet produces grain, and hence there is a single row of grains on each side of the rachis. In the six-rowed forms all the spikelets produce grain, leading to the development of three rows of grain on each side. By crossing two- and six-rowed varieties, all forms are found in the offspring from the development of grain in the central spikelet on each side only, to the development of grain by all three spikelets; also forms occur in which the normally fertile central spikelet becomes barren and only the lateral ones are fertile. This leads to a four-rowed barley the only truly four-rowed form known, the so-called four-rowed barleys of commerce being only irregular forms of the six-rowed types. A point of some interest is found in connection with these hybrid barleys. In the earlier generations of many of these six-rowed hybrids, the lateral grains are very much smaller than the central ones that is they contain much less endosperm. But by collecting the small lateral grains and growing them separately the progeny is as vigorous vegetatively and reproductively, and gives as great a percentage of germinating grains as the progeny from the lai-ge central grains. Indeed, cultivation has led to the development of more endosperm in the grain than is necessary for the nutriment of the young plant. A hulled barley is one in which the pales adhere to the ripe grain. In a hull-less barley the grains are free. In the hulled forms the stamens though detached at the base are not completely thrown out, but are held by the pales. They seem to serve as a point of attack for fungal parasites, the mycelium then invading the grain. In hull-less forms the danger is obviated as the anthers are completely shed. In the hulled varieties the style also persists and seems to serve as a second point of fungal attack. All forms found

5 Notes on Cereals. 21 in the hulled varieties have been produced also by appropriate composite crossing in the hull-less forms also. There are certain varieties of barley in which the awns fall off on ripening. These are termed beardless barleys. When the beard falls off, the apex of the grain is exposed to the attacks of fungi. In the long-bearded forms which return their awns there is danger of interlocking of the awns and consequent levering off of the grains. An attempt is now being made by Mr. Garton to produce shortly awned varieties with the best quality of grain. Plants in the sporting stage are more susceptible to fungal attacks than are the fixed breeds. Crossing different breeds of barley leads to practically no sterility. In wheats the crossing of extreme forms introduces some lessening of the fertility, and in oats it often leads to a considerable degree of sterility. OATS. Dull weather at the time of pollination in Oats may lead to a loss of 25% in the yield of the crop. Such sterility is generally to be traced to the inactivity of the pollen grains. The w'iki A vena fatita, however, produces fertile anthers and active pollen grains even in very dull weather. This plant is extremely fertile in the wild state, most of the flowers producing grain. It has been extensively used at Acton Grange as a parent in composite crossing, since it leads to the production of a larger percentage of flowers with fertile anthers and also to a greater yield of grain. In the Oat-spikelet the lower grains are larger than the upper ones. These two forms have been collected and sown separately. The resulting crop shows that the smaller ones are as fertile in every way as the larger ones, and that in the latter the young plant attains its independence long before the whole supply of endosperm has been absorbed. In Aveiia fattia, however, practically all the endosperm is required.

6