GENETICS 323 



is yet known. But leaving the question of curl on one side, we have 

 in regard to the length and fineness of wool, a problem which genetic 

 experiment ought to be able to solve. Note that in it, as in almost all 

 problems of the " yield " of any product of farm or garden, two distinct 

 elements are concerned — the one is size, and the other is number. The 

 length of the hair is determined by the rate of excretion and length of 

 the period of activity of the hair follicles, but the fineness is determined 

 by the number of follicles in unit area. Now analogy is never a safe 

 guide, but I think if we had before us the results of really critical ex- 

 periments 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 pos- 

 sible 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 

 luster depends, but I incline to think it is an expression of fineness of 

 fiber, which again is probably a consequence of the smallness and in- 

 creased number of the excreting cells, somewhat as the fineness of wool 

 is a consequence of the increased number and smallness of the ex- 

 creting follicles. 



Again the question arises in regard to flax, how should a strain be 

 bred which shall combine the maximum length with maximum fineness 

 of fiber ? The element of number comes in here, not merely with regard 

 to the number of fibers in a stem, but also in two other considerations, 

 first, that the plant should not tiller at the base, and, secondly, that the 

 decussation of the flowering branches should be postponed to the highest 

 possible level. 



Now in this problem of the flax, and not impossibly in the others I 

 have named, we have questions winch 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 may show the way into some of 

 those general problems 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 behavior of these 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, that the increased number is a consequence of the removal 

 of a factor which prevents or inhibits particular divisions, so that they 



