402 PHYSIOLOGY OF GROWTH. 



The buds of willow shoots, e.g., develop very rapidly, as also do 

 those of Syringa (I found that in the hothouse, twigs cut towards 

 the end of February had unfolded their leaves completely in less 

 than fourteen days), while the buds of Laburnum do not succeed 

 in unfolding quite so easily. Experiments made at different parts 

 of the winter, and with different plants, furnish results which are 

 interesting in many respects. We only require for such experi- 

 ments large branches or twigs, placed with their lower ends in 

 water, care being taken that the air around the plants is not too 

 dry, to ensure which it is generally better to conduct the experi- 

 ments in the hothouse than in the room. 



If we take potatoes into a warm room in autumn, and leave 

 them there in a box, we find that they do not begin to germinate 

 till about the new year. A resting period is thus characteristic of 

 potatoes, as also of buds. Miiller-Thurgau 1 has attempted to 

 determine the cause of this resting period, and I 2 have occupied 

 myself with the same question. If after they have been lying in 

 the room for some time, we examine the potatoes for sugar, by 

 rubbing some of them on a grater, adding water to the pulp, and 

 then after a time filtering off the fluid and testing it with Fehling's 

 solution, we shall find no glucose or only traces of it. In January, 

 when the tubers begin to germinate, the quantity of sugar they 

 contain is still very small ; it gradually, however, becomes con- 

 siderable. If in December we treat a small quantity (20 c.c.) of 

 the fluid obtained from potatoes with a little thin starch paste, 

 the presence of diastase cannot with certainty be demonstrated 

 (for method, see 112). Potatoes far advanced in germination, 

 however, certainly do, as I satisfied myself, contain diastase. 



From this we may assume that the reason the potatoes do not 

 at once germinate in the autumn, is that they are not able to pro- 

 duce quantities of diastase sufficient for abundant production of 

 sugar. The quantities of sugar formed in the tubers in autumn 

 suffice, it is true, to maintain their respiration ; but the sugar 

 does not accumulate to any marked extent in the tissues, and is 

 not sufficient to ensure energetic growth of the buds. Gradu- 

 ally more and more diastase is formed in the tubers; larger 

 quantities of sugar are produced, and germination can begin. It 

 is very probable that the results to which we are led in studying 

 the resting period of potatoes are of significance in explaining the 

 resting period of the winter buds of our trees and shrubs, and this 

 adds interest to the following experiment of Miiller-Thurgau. 



