190 



FIRST YEAR SCIENCE 



of a thickened bulb like the onion (Fig. 87) ; some, like 

 the cacti, assume a fleshy leaflike, though leafless form ; 

 some, like the nut grass, Johnson grass and 

 witch grass, grow underground and send 

 up shoots, and some stems store up food 

 underground in tubers, like the potato 

 (Fig. 87), from which the next year's 

 plant may grow. 



Notwithstanding all the diversity shown 

 by the stem, its principal functions are to 

 support the leaves, so that they will best 

 be exposed to the light, and to conduct 

 the food solutions from the root to the 

 leaves. The part of the stem through 

 which the cell sap flows was seen in 

 Experiments 95 and 96. 



There are two great types of stems, one 

 represented by the corn stalk and palm 

 and the other by the willow, sunflower and 

 bean. On account of the structure of the 

 seeds these are called, respectively, mono- 

 cotyledonous (one seed leaf) and dicotyledonous (two seed 

 leaves). That these differ greatly in their appearance 

 was seen in Experiments 95 

 and 96, where the two kinds 

 of stems were compared. It 

 was also found in these ex- 

 periments that, in the first, 

 the red colored water that 



took the place of the sap rose in the fibrous bundles scat- 

 tered through the pith, while in the second it rose through 

 the woody tissue within the bark. 



Experiment 97. Examine a cross section of a hardwood tree 

 several years old, and if possible of a palm. Notice the ring-like 



AN IVY BRANCH. 



Notice the tiny 

 root-like ap- 

 pendages by 

 which it clings 

 to its support. 



