40 



COLLEGE BOTANY 



against extremes of temperature but against water, which would 

 be injurious under almost any conditions. In some cases the 



FIG. 17. The rhizome or rootstock type of stem. 



gum is bitter and may serve as a protection against, animals 

 which would eat them for food. When the leafy shoot elongates, 



FIG. 18. The tuber type the potato. 



the outer scales are shed and the leaves grow and expand very 

 rapidly (Figs. 20 and 21). The scales and leaves are borne 



