174 



DIVISION OF LABOR 



roundings. Later, when conditions become favorable for its 



germination, the spore may form a new filament of pond scum. 

 . .. In molds, in yeasts, and in the bacteria we also 

 X/""/ found spores coulct be formed by the protoplasm 

 of the plant cutting up into a number of tiny 

 spores. These spores are called asexual (without 

 sex) because they are not forni'ed by the union 

 of two cells, and may give rise to other tiny 

 plants like themselves. Still other plants, mosses 

 and ferns, give rise to two kinds of spores, sexual 

 and asexual. All of these collectively are called 

 spore plants. 



Reproduction in Seed Plants. Another great 

 group of plants we have studied, plants of varied 

 shapes and sizes, produce 

 seeds. They bear flowers 

 and fruits. 



The embryo develops 

 from a single fertilized 

 " egg," growing by cell 

 division into two, four, 



eight, and a constantly increasing number 



of cells until after a time a baby plant is 



formed, which as in the bean, either con- 

 tains some stored food to give it a start 



in life, or, as in the corn, is surrounded 



with food which it can digest and absorb 



into its own tiny body. We have seen 



that these young plants in the seed are 



able to develop when conditions are favor- 

 able. Furthermore, the young of each 



kind of plant will eventually develop into 



the kind of plant its parent was and into 



no other kind. Thus the plant world is 



divided into many tribes or groups. 



Plants are placed in Groups. If we plant a number of peas so 



that they will all germinate under the same conditions of soil, tern- 



The formation of 

 spores in pond 

 scum, zs, zygo- 

 spore; /, fusion 

 in progress. 



The formation and growth of 

 a plant embryo. 1, the 

 sperm and egg cell uniting; 

 2, a fertilized egg; 3, two 

 cells formed by division; 

 4, four cells formed from 

 two ; 5, a many-celled 

 embryo; 6, young plant; 

 H, hypocotyl; P, plumule; 

 C, cotyledons. 



