CHAPTER XXIII 



FIG. 254. CHRISTMAS FERN. 

 Dryopteris acrostichoides ; 

 known also as Aspidium. 



PHENOGAMS AND CRYPTOGAMS 



THE plants thus far studied produce flowers; and the 



flowers produce seeds by means of which the plant is prop- 

 agated. There are other plants, 

 however, that produce no seeds, 

 and these plants (including bac- 

 teria) are probably more numer- 

 ous than the seed-bearing plants. 

 These plants propagate by means 

 of spores, which are generative cells, 

 usually simple, containing no em- 

 bryo. These spores are very small, 

 and sometimes are not visible to 

 the naked eye. 



Prominent among the spore- 

 propagated plants are ferns. The 



common Christmas fern (so called 



because it remains green during 



winter) is shown in Fig. 254. The 



plant has no trunk. The leaves 



spring directly from the ground. 



The leaves of ferns are called 



fronds. They vary in shape, as 



other leaves do. Some of the 



fronds in Fig. 254 are seen to be 



narrower at the top. If these are 



examined more closely (Fig. 255), 



176 



FIG. 255. FRUITING FROND 

 OF CHRISTMAS FERN. 



Sori at a. One sorus with its in- 

 dusium at b. 



