54 



STEMS 



beauty, the tulip, and the skunk cabbage, owe their early bloom- 

 ing habit to richly stored underground stems of some kind, or 

 to thick fleshy roots. Many of these very early blooming plants 

 are woodland species which must hurry through most of the 

 season's growth and begin to mature seed before the shade of 

 the trees above them cuts off most of the necessary supply 

 of light and before the drought of summer begins. 



67. Condensed stems. The plants of desert regions require, 

 above all, protection from the extreme dryness of the surround- 



FIG. 50. A globular cactus 



ing air, and usually from the excessive heat of the sun. Ac- 

 cordingly, many desert plants are found quite destitute of ordi- 

 nary foliage, exposing to the air only a small surface. In the 

 globular cactuses (Fig. 50) the stem appears reduced to the 

 shape in which the least possible surface is presented by a plant 

 of given bulk, - - that is, in a somewhat spherical form. Other 



