January, 1912.] 



19 



Scientific Agriculture, 



critical experiments on the genetics of 

 size and number of multiple organs in 

 any animal or even any plant, we might 

 not wholly be at a loss in dealing with 

 this important problem. 



A somewhat similar question comes 

 from South Africa. Is it possible to 

 combine the qualities of a strain of 

 ostriches which has extra long plumes 

 with those of another strain which has 

 its plumes extra lustrous ? I have not 

 been able fully to satisfy myself upon 

 what the lustre depends, but I incline to 

 think it is an expression of fineness of 

 fibre, which again is probably a conse- 

 quence of the smallness and increased 

 number of the excreting cells, somewhat 

 as the fineness of wool is a consequence 

 of the increased number and smallness 

 of the excreting follicles. 



Aeain the question arises in regard 

 to flax, how should a strain be bred 

 which shall combine the maximum 

 length with maximum fineness of fibre ? 

 The element of number comes in here, 

 not merely with regard to the number 

 of fibres in a stem, but also in two other 

 considerations : first, that the plant 

 should not tiller at the base, and, second- 

 ly, that the decussation of the flowering 

 brauches should be postponed to the 

 highest possible level. 



Now in this problem of the flax, and 

 not impossibly in the otheis I have 

 named, we have questions which can in 

 all likelihood be solved in a form which 

 will be of general, if not of universal, 

 application to a host of other cognate 

 questions. By good luck the required 

 type of flax may be struck at once, in 

 which case it may be fixed by ordinary 

 Mendelian analysis, but if the problem is 

 investigated by accurate methods on a 

 large scale, the results oaay show the 

 way into some of those general prob- 

 lems of size and number which make a 

 great part of the fundamental mystery 

 of growth. 



I see no reason why these things 

 should remain inscrutable. There is 

 indeed a little light already. We are well 

 acquainted with a few examples in 

 which the genetic behaviour of those 

 properties is fairly definite. We have 

 examples in which, when two varieties 

 differing in number of divisions are 

 crossed, the lower number dominates — 

 or, in other words, the increased num- 

 ber is a consequence of the removal 

 of a factor which prevents or inhibits 

 particular divisions, so that they do not 

 take place. It is likely that in so far as 

 the increased productivity of a domesti- 

 cated form as compared with its wild ori- 

 ginal depends on more frequent division, 

 7 



the increase is due to loss of inhibiting 

 factors. How far may this reasoning be 

 extended? Again, we know that in sever- 

 al plants — peas, sweet-peas, Antirrhi- 

 num, and certain wheats — a tall variety 

 differs in that respect from a dwarf in 

 possessing one more factor. It would be 

 an extraordinarily valuable addition to 

 knowledge if we could ascertain exactly 

 how this factor operates, how much of 

 its action is due to linear repetition, 

 and how much to actual extension of 

 individual parts. The analysis of the 

 plants of intermediate size has never 

 been properly attempted, but would be 

 full of interest and have innumerable 

 bearings on other cases in animals and 

 plants, some of much economic im- 

 portance. 



That in all such examples the objective 

 phenomena we see are primarily the 

 consequence of the interaction of genetic 

 factors is almost certain. The lay mind 

 is at first disposed, as always, to attri- 

 bute such distinctions to anything rather 

 than to a specific cau^e which is invisible. 

 An appeal to differences in conditions — 

 which a moment's reflection shows to 

 be either imaginary or altogether inde- 

 pendent — or to those vague influences 

 invoked under the name of selection, 

 silently postponing any laborious ana- 

 lysis of the nature of the material 

 selected, repels curiosity for a time, and 

 is lifted as a veil before the actual pheno- 

 mena ; and so even critical intelligences 

 may for an indefinite time be satisfied 

 that there is no specific problem to be 

 investigated, in the same facile way 

 that, till a few years ago, we are all 

 content with the belief that malarial 

 fevers could be referred to any damp 

 exhalations in the atmosphere, or that 

 in suppuration the body was discharging 

 its natural humours. In the economics 

 of breeding, a thousand such phenomena 

 are similarly waiting for analysis and 

 ref ei ence to their specific causes. What, 

 for instance, is self-sterility ? The pheno- 

 menon is very widely spread among 

 plants, and is far commoner than most 

 people suppose who have not specially 

 looked for it. Why is it that the pollen 

 of an individual in these plants fails to 

 f ertilise the ova of the same individual ? 

 Assexual multiplication seems in no 

 way to affect the case. The American 

 experimenters are doubtless right in 

 attributing the failure of large plant- 

 ations of a single variety of apples or 

 of pears in a high degree to this cause. 

 Sometimes, as Mr. W. O. Backhouse has 

 found in his work on plums at the John 

 Innes Horticultural Institution, the be- 

 haviour of the varieties is most definite 

 and specific. He carefully self -fertilised 



