Buds and Stems. . 69 



up of new tissues. The reserve materials can be demon- 

 strated by using tests for starch, proteids, sugar, oils, etc., 

 chiefly in the medullary rays and wood parenchyma cells 

 of the stems and underground parts. Before these mate- 

 rials are needed in the spring, those which are insoluble or 

 poorly diffusible are changed by appropriate ferments so 

 that they can pass by diffusion from cell to cell, or be carried 

 more rapidly upward by the ascending currents of water. 

 Buds which remain attached to the parent plant and are 

 able to draw upon it for their food do not need to have the 

 reserve materials stored within their own tissues, as in the 

 case of seeds which are cast off from the parent and left 

 thereafter to shift for themselves. 



52. Leaf and Flower Buds. Dissection of the terminal 

 buds of the horse-chestnut reveals the fact that many of them 

 contain flowers as well as leaves, while the terminal buds 

 of the lilac may contain only flowers. In the cottonwood 

 we find many of the lateral buds containing flowers only, 

 while the terminal buds contain only leaves. When we 

 inquire the reason why the growing point of certain form- 

 ing buds gives rise to leaves and that of others to flowers, 

 or to both leaves and flowers, we are unable to obtain a 

 satisfactory answer. We know, however, that some peren- 

 nial plants produce only leaf buds for a number of years, 

 and are not able to form flowers until they have attained a 

 certain age ; we do not expect apple trees, for instance, to 

 bear flowers until they are five years old or more. The 

 century plant does not produce flowers until it has attained 

 an age of twenty to thirty years. We know, too, that 

 shoots which would otherwise terminate with winter budk 

 containing leaves only can be made to terminate with buds 

 containing flowers if the branch on which the shoot is 

 borne is pruned back, or if the roots are pruned. By this 



