90 REGENERA TION 



may be made. Its presence in larger or smaller quantities may 

 determine what a particular part shall become, but further than 

 this it exerts no specific action. This means that the presence of a 

 certain amount of food substance may determine what a given region 

 shall produce, but it is not supposed that there are different kinds of 

 food materials that correspond to each kind of structure. If there 

 were such, they would not differ from specific substances, unless we 

 wish to make subtle distinctions without any basis of fact to go upon. 



Goebel points out that there is evidence to show that the greater 

 or less quantity of food substance contained in a plant often deter- 

 mines the nature of its growth, as for instance the production of 

 flowers when the food supply runs low and the production of foliage 

 when the food supply is abundant. This difference may explain 

 Sachs' experiment with begonia leaves ; and if so, there is no need 

 for supposing specific flower stuffs to be made in the plant. 



There is another point of view which has been, I think, too much 

 neglected, viz. that the production of food stuffs is itself an expression 

 of changes taking place in the living tissues, and if the structure 

 is changed so that it no longer produces the same substances it 

 may then lead to the development of different kinds of organs. The 

 difference in the regeneration of an apical and a basal leaf of begonia 

 may be due to some difference in the structure of the protoplasm. 

 The greater or smaller amount of starch produced in these leaves may 

 be only a measure of, and not a factor in, the result. 



In this same connection another question needs to be discussed. 

 It is assumed by several botanists that in a normal plant the latent 

 shoots or buds along the stem do not develop so long as the terminal 

 shoots are growing, because the latter use up all the food material 

 that is carried to that region. If the terminal bud is destroyed the 

 lateral shoots then burst forth, in consequence, it is assumed, of the 

 excess of food stuff that now comes to them. I do not believe that 

 the phenomena can be so easily explained. If a piece of a plant is 

 cut off, the leaves removed, and the piece suspended in a moist 

 chamber and kept in the dark, the lateral buds at the apex will begin 

 to develop. If we assume that the piece cannot develop any new 

 food substance in the dark, then it contains just the same amount 

 as it did while a part of the plant, and yet that amount is ample for 

 the development of the lateral buds. Moreover, only the more apical 

 buds develop ; but if the piece is then cut in two, the apical buds of 

 the basal piece, that had remained undeveloped, will now develop. 

 How can this be explained by the amount of food substances in the 

 piece ? If it is assumed that in the normal plant the food substances 

 flow only to the growing points, and the buds are out of the main cur- 

 rent and fail in consequence to develop, it can be shown that this 



