6o4 



NATURE 



[January 28, 19 15 



contained in the light, for it does not succeed 

 in storing up in the shape of plant materials 

 it produces as much as i per cent, of the energy 

 that falls upon it as light, and in bright, tropical 

 light the percentage utilised is even less. A steam 

 engine, given a certain amount of energy in the 

 shape of coal, turns out again about one-seventh of 

 it in the shape of useful work ; a gas or oil engine is 

 an even more effective transformer. Can the duty of 

 the leaf be increased so that it shall effect a greater 

 production of dry matter for the amount of light 

 energy it receives? We know very little as yet about 

 even the sequence of chemical changes in the leaf 

 beyond the fact that we begin with carbon dioxide 

 and water and end with oxygen and some sort of 

 sugar, we are beginning to acquire knowledge as to 

 the extent the rate of change is affected by the supply 

 of light, carbon dioxide, and water, and by the tem- 

 perature. But we have now many examples in chem- 

 istry of reactions being speeded up or rendered more 

 complete by means of some adjustment of the external 

 conditions, so it is perhaps not too much to expect 

 that this fundamental process of carbon assimilation 

 may also be tuned up until the leaf becomes of greater 

 efficiency than at present in producing tissue from the 

 materials and energy supplied to it. 



Probably the most immediate successes are before 

 the plant-breeder, now that the application of the 

 Mendelian theory has provided a method which renders 

 both speedy and certain the processes of crossing and 

 selection whereby the practical men of the past, work- 

 ing almost at haphazard, have already effected such 

 enormous improvements in our cultivated plants. 

 Among cereals, the qualities in demand, qualities 

 which we know to be obtainable, are resistance to 

 disease, stiffness of straw, and a large migration 

 factor. We want to. get rid of the plant-doctor, as it 

 were ; spraying and other prevention or curative treat- 

 ments are both costly and of limited efficacy ; the 

 desirable method is to keep the plant free of disease 

 by means of a naturally resistant constitution, and by 

 establishing healthy conditions of soil and nutrition. 

 As to stiffness of straw, the incapacity to stand up is 

 probably the chief cause which limits the yield of corn 

 crops in Britain wherever the farming is high.. When 

 a man keeps much stock, and buys cake either for his 

 bullocks, or to feed to his sheep on the turnips, the 

 land becomes so rich that the first corn crop will only 

 stand up under exceptionally favourable weather con- 

 ditions, and the farmer, so far from buying more 

 fertiliser, cannot take full advantage of what is already 

 in the soil. The land is often rich enough to yield 

 60 bushels of wheat to the acre, but it is exceptional 

 that a crop of such weight will stand uo so that it can 

 be harvested b}' a self-binder. Mr. Beaven, in this 

 section, has already dealt with migration ; clearly it 

 is a matter of great importance to the plant-breeder. 

 Though the details have onlv been worked out for 

 barley, the different varieties .of any cultivated plant, 

 wheat, for example, are very much alike as regards 

 their gross productive power — \.e. the whole material 

 grown weighs much the same in a dried condition. 

 Even different crops produce much the same amount 

 of dry matter when grown under the same conditions, 

 this gross productive power being in all cases the 

 similar product of the environment — \.e. the result 

 arising from the supply of food, water, light, tempera- 

 ture, etc. But granted that the different crops possess 

 this same gross productive power, then their com- 

 parative usefulness depends upon the greater or less 

 completeness with which they transform the crude 

 material into products that may be used as food for 

 man. In the cereals, for example, we want as much 

 as possible of the original stuff manufactured by the 

 leaf to be migrated later in the plant's life into the 

 NO. 2361, VOL. 94] 



seed; of the total weight of the crop we want the 

 largest possible proportion to be high-grade grain and 

 not low-grade straw. Mr. Beaven has shown that 

 the various varieties of barley do differ constantly 

 in their projxDrtion of grain to straw, and as, without 

 doubt, the same differences hold for other crops, this 

 is a matter which must be watched by the plant- 

 breeder. 



Cereals are not, however, the only materials upon 

 which the plant-breeder has to work; indeed, they are 

 alreadv among the most advanced of our domesticated 

 plantsj and the other farm crops require great improve- 

 ment before they reach the level of wheat and oats. 

 Sugar beet affords a most interesting case ; by selec- 

 tion the percentage of sugar contained in the root has 

 been raised by one-half. The total amount of material 

 grown per acre remains, however, much where it 

 was, because of the difficulty, the impossibility, in 

 fact, as yet, of testing the yielding capacity of a 

 seedling root whereas its sugar contents can be 

 measured with ease. The same difficulty is seen 

 among our other root crops ; such improvement as has 

 been effected in the mangold, turnip, etc., has chiefly 

 been in the shapeliness and habit of growth of the 

 root, these alone being the characters that are apparent 

 to the selector dealing with a group of seedlings. 

 To some extent these may be correlated with total 

 vield, but how little may be judged from the fact that 

 the long red mangold, one of the very oldest varieties, 

 is still the largest producer of dry matter and sugar 

 per acre. The comparative 3-ield of cereal varieties 

 mav be tested by the growth of a few hundred plants 

 under rigorous conditions ; some similar method will 

 have to be worked out for root and fodder crops, 

 before the plant-breeder can make much headway with 

 them. Granted such a method, the plant-breeder has 

 a fine, unexplored field before him in the leguminous 

 and cruciferous fodder crops, and again in the fibre 

 plants. Commercial flax, for example, is an entirely 

 heterogeneous mixture of varieties, which never 

 appears to have been subjected to the most ordinary 

 selection. The fodder crops are matters of immediate 

 importance ; because the more intensive cultivation of 

 the w^estern side of Great Britain, where the high 

 rainfall renders the growth of cereals a somewhat 

 speculative industry, subject to loss at harvest and 

 difficulties in the spring preparations for sowing, de- 

 pends upon the elaboration of a system of farming 

 based upon rapidly growing fodder crops. At present 

 these districts produce milk, meat, and store stock, 

 niainlv from grass land that gets but little aid from 

 the cultivator. The gross productive power of such 

 land is small, and under the plough can be enor- 

 mously raised, but arable farming has hitherto been 

 avoided, except at times of abnormal prices, because 

 of the risks attending harvesting. With improved 

 fodder crops in place of grain a more profitable system 

 of husbandry would replace the crops, .\gain, a new 

 countrv like Australia will have to evolve its own 

 fodder crops to suit the climate, and its own soil 

 regenerating plants. 



Despite the fact that a given area of land will 

 produce somethiner like ten times as much human 

 food of a vegetable nature as of meat and milk, if 

 mere power of supporting life is considered, we may 

 assume that the human race will not for a long time, 

 if ever, turn to vegetarianism. Absolute pressure of 

 population, supposing the maximum has to be sup- 

 ported that the land can be made to carry, would put 

 an end to the preliminary conversion of vegetable 

 into animal food, but it is probable that the dominant 

 races will insist on remaining flesh-eaters even if that 

 necessitates the limitation of their own numbers. 

 However, the scientific man has at present little to 

 sav to this sociological question ; his business is to 



