PHYSIOLOGY. 



Bulbs, usually underground, short, conic, leaf and scale bearing; ex., 

 lily. 



Thorns, stout, thick, poorly developed bran- 

 ches with rudiments of leaves (scales); ex., 

 hawthorn. 



Tendrils, slender reduced stems. 



Flower axes (see morphology of the angio- 

 sperms). 



174. Leaf series. Besides the foliage leaves, 

 the following are some of their modifications: 



Flower parts (see morphology of the angio- 

 sperms). 



tracts and scales, small, the former usually 

 green (flower bracts), the latter usually chloro- 

 phylless. Bud scales are sometimes green. 



Tendrils, modifications of the entire leaf 

 (tendrils of the squash where the branched 

 tendril shows the principal veins of the leaf), 

 modification of the terminal pinnae of the leaf 

 (vetch), etc. 



Spines (examples are found in the cacti, 

 where the stem is enlarged and green, function- 

 ing as a leaf). 



Other modifications occur as in the pitcher 

 plant, insectivorous plants, etc. 



175. The root shows less modification. Be- 

 sides normal roots, which are fibrous in most 

 small plants and stout in the larger ones, some 

 of the modifications are found in fleshy roots, 

 where nourishment is stored (ex., dahlia, 



Fig. 64. sweet potato, etc.), aerial roots (ex., poison 



Female plant (gametophyte) of ivy t h e twining form), aerial orchids, etc. For 

 a moss (mmum), showing rhizoids "' 

 below, and the tuft of leaves above, modifications of roots due to symbiotic fungi, 



see chapter on Nutrition in Part III. 



which protect the archegonia. 



