ARTIFICIAL AND NATURAL SELECTION 37 



least in large part, a process in which the various organs of a plant 

 act more or less independently. This form of variability is there- 

 fore to be distinguished by the term of "partial fluctuation." 



Opposed to it stands the individual variation, which affects the 

 whole individual in the same manner, but which influences different 

 individuals in different degrees and ways. If this individual fluctua- 

 tion is a response to outer influences too, the question arises, when 

 do they work, and at which period of its development does the 

 organism respond to them. 



Here for our discussion plants afford great advantages over ani- 

 mals. For it is clear that, as soon as buds are produced, partial fluctu- 

 ation must prevail and individual variation become reduced. There- 

 fore only the embryonic stage pertains to the latter, whilst the 

 whole subsequent life is ruled by partial responses. The embryo 

 itself leads its life within the seed, and thus we are induced to 

 consider the period of the ripening of the seed as one of prominent 

 significance for the whole group of phenomena collected under the 

 name of fluctuations. 



The life of the germ commences with the copulation of the male 

 and female sexual cells. Obviously even these must vary, since they 

 have been previously subjected to varying conditions. The individual 

 characters of a given organism must, therefore, largely depend upon 

 the degree of development of latent qualities, already present in the 

 sexual cells before their copulation. And it is equally manifest that 

 at that important moment there is as yet no room for partial fluctua- 

 tion. 



As soon, however, as tissues are developed, the chances for the 

 latter arise and rapidly increase, whilst in the same degree the part 

 of the individual variability must decrease. Leaving aside the buds 

 in the axils of the cotyles, and equally discarding the primary root, 

 we may limit our interest to the terminal vegetative cone of the 

 young plant, and consider all variations therein provoked as of. 

 individual nature. 



But as soon as this cone begins to differentiate itself, individuality 

 comes to an end, at least in respect to the responses to varying 

 agents, and partiality takes its place. In the same measure the 

 embryonic life is replaced by that of the developing plant. Thus we 

 might call the individual fluctuation by the name of embryonic 

 fluctuation, if it is only rightly understood that the variations of the 

 paternal and maternal cells before their copulation are to be included. 



In horticultural practice individual and partial fluctuation play 

 a very large part. Excluding the embryonic stage from the process 

 of multiplication, the embryonic variability may be excluded, too. 

 Hence the almost universal use of vegetative multiplication in all 

 cases where it is practically applicable. Perennial plants and shrubs 



