MORPHOLOGY OF LEAVES AND FLOWERS 



623 



The two groups of higher seed plants, or Angiosperms, differ 

 widely in the structure of the embryo. In the group including the 

 grasses, rushes, sedges and such plants as wild onion (Allium 

 canadense) the globular embryo soon develops into an axis with 

 the root tip at one end and one cotyledon at the other. The stem 

 tip arises from the side of the axis as a lateral member. This 

 group of plants is designated as Monocotyledons (one cotyledon). 



Pig. 487 I Fig. 487 II Fig. 488 



Fig. 487. I. Fruit of Squaw-weed (Senecio). II. Fruit of Dandelion. Each 

 is crowned with pappus which aids in distribution. 

 (After Thome.) 



Fig. 488. The fruit of the Winter Cherry (Physalis) with a portion of the 



inflated calyx removed to show the enclosed berry. 



(After Thome.) 



In the other group, to which a large number of the weeds be- 

 long, the axis of the embryo develops a root tip at one end, a stem 

 tip at the other, and a pair of cotyledons, one on each side of the 

 stem tip. Since two is the prevailing number of cotyledons, the 

 term Dicotyledons is applied to this group. 



Fig. 489 Fig. 490 



Fig. 489. I. Fruit (pod) of Plantain with upper portion of pod breaking 

 and falling off to allow seeds to escape. II. Pod of Poppy opening by 

 a lid. 



(After Thome\) 



Fig. 490. Fruit of Mallow which separates into as many one-seeded carpels 



as there are styles. 

 (After Thome.) 



