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 expana very 

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



