56 



ACKOXO.MV 



-cyto 



a roothold and access to the light and air, while mosses, ferns, 

 and fungi grow among and upon them. This great diversity 

 of form makes it necessary to place the plants in different 

 groups, according to their common characteristics, and bota- 

 nists generally make four great groups of this kind. First and 

 simplest in structure are the TkaUophytes, comprising the algae, 

 fungi, and bacteria. None of these have true leaves or stems, 

 or produce either flowers or fruits. Next above these come 

 the Bryophytef, which include the mosses and liverworts. 

 They are somewhat more highly organ- 

 ized than the thallophytes, but are like 

 them in lacking true leaves, flowers, 

 and fruits. The Pteridophytes consist of 

 the ferns and their allies. These plants 

 have stems and leaves, and some spe- 

 cies bear structures that are essentially 

 flowers, but none bear seeds. Last and 

 most highly specialized are the Sper- 

 matophytes, or true flowering plants, 

 which are distinguished from all the 

 others by the production of seeds. 



Only two of these groups are of 

 much interest to the farmer and gar- 

 dener. The thallophytes have to be 

 taken into account because from their 

 ranks come not only the bacteria that 

 flavor cheese, butter, and other prod- 

 ucts, turn cider to vinegar, and render 

 soils fertile, but also the multitudes 

 of plant diseases and fungus pests that injure the cultivated 

 crops, destroy our foods, cause disease in the lower animals, 

 and even attack man himself. The cultivated plants, however, 

 are spermatophytes, and so are the weeds that struggle with 

 them for the possession of the soil. The word spermatophyte 



Icell w 



FIG. 29. An epidermal hair 



from the bracken showing 



the cells 



cell w, cell wall ; cyto, cyto- 

 plasm; nit, nucleus; s, starch 

 grains 



