Oct. is, 1920 Influence of Cold in Stimulating Growth of Plants 155 



5. The; theory advanced in explanation of the formation of 

 sugar during the process of chilling is that the starch grains 

 stored in the cells of the plant are at first separated by the 

 living and active cell membranes from the enzym that would 

 transform the starch into sugar, but when the plant is chilled 

 the vital activity of the cell membrane is weakened so that the 

 enzym "leaks" through it, comes in contact with the starch, 

 and turns it into sugar. 



I have stated the theory in these words out of regard for simplicity 

 and general understanding, but if anyone should require that it be pre- 

 sented in orthodox technical language it might be restated as follows: 

 The reserve amylum carbohydrate bodies are isolated from the amylo- 

 lytic enzym by semipermeable protoplasmic living membranes of high 

 osmotic efficiency, but under the influence of low temperatures the pro- 

 toplasmic membranes are proximately devitalized, they become per- 

 meable to the amylolytic enzym, and amylolysis ensues. I may add, 

 however, that the use of such terminology seems to me to involve a cer- 

 tain degree of unnecessary cruelty. 



From the evidence already presented, no one, presumably, will question 

 that the chilling of dormant trees and shrubs is followed by growth and 

 that the growth is associated with the transformation of starch into sugar. 

 But the hypothesis that this transformation is brought about by the 

 weakening of the cell membrane and the consequent leakage of starch - 

 transforming enzyms into the starch chambers may very properly be 

 challenged. In the Tropics there is no chilling weather, yet trees and 

 shrubs spring into growth after the dormant period of the dry sea- 

 son just as they do in temperate climates after the dormant period of 

 winter. The critical scientific man will therefore ask, "Are there not 

 other agencies than chilling which will start dormant trees and shrubs 

 into growth even in our latitude?" It must be said in reply that there 

 are. And it will be worth while to consider some of these causes, for 

 not only are they of interest in themselves but also, instead of weakening 

 the hypothesis here presented, they serve to strengthen and confirm it. 



The data may best be presented through a series of illustrations. 



The pruning of a long-dormant plant will often start it into growth 

 (PI. 25, A). Girdling produces a similar result (PI. 25, B, at left). 

 Notching the stem does the same (PI. 25, B, at right). Rubbing the 

 stem also starts the plant into growth (PI. 26). 



In all these examples of the stimulation of growth by injury it is con- 

 ceived that the enzym is brought into contact with the starch as a direct 

 result of the breaking and straining of the cells. Sugar is then formed 

 and growth begins. 



It should be observed that when a normal chilled plant starts growing 

 it grows from many buds (PI. 27, A), for the effect of the chilling on sugar 

 formation is general. When a dormant plant starts growing as the result 



