THE SPOROPHYTE 277 



(venter) becomes the single egg, while the others in the neck 

 region (Fig. 244, ri), called canal cells, break down and their 

 substance becomes changed into mucilage. The archegonia, like 

 the antheridia, open only when wet, the cells at the tip separat- 

 ing so as to give a clear passage for the entrance of the sperms 

 into the neck. The sperms are attracted to the opening by cer- 

 tain substances such as sugar contained in the liquefying muci- 

 lage. The sperms swim down the neck, and one of them, fusing 

 with the egg, fertilizes it. There is much evidence that the 

 canal cells are degenerate gametes, and that the archegonium 

 came from a type of sexual organ that originally produced a 

 number of gametes, as does the antheridium. 



284. The sporophyte. The term sporophyte has appeared 

 before in the accounts of the red algae (Sec. 246) and sac fungi 

 (Sees. 266, 272) where certain peculiar fructifications (cystocarps 

 and ascocarps), following the sexual process, alternated with the 

 sexual plants. The sporophytes of the liverworts and mosses 

 have a similar position in the life history, and are likewise 

 borne on the parent plants and frequently called their " fruits." 



The sporophyte of the liverworts and mosses develops at 

 once from the fertilized egg, which never becomes a resting 

 spore (oospore), as in the algae. The form is various in differ- 

 ent groups. Most of the mosses have long, stalked sporophytes 

 (Figs. 261, 265), which end in swollen spore cases. The liver- 

 worts generally have much smaller sporophytes, some of which 

 have no stalk at all and consist of the spore case alone. If the 

 sporophyte is small it may remain inclosed in the base of the 

 archegonium, which becomes much enlarged. But the stalked 

 sporophytes either burst out of the archegonium, or frequently, 

 as in the common mosses, tear it off and carry it upwards as a 

 cap-like structure (Fig. 265, B,cal) called the calyptra (meaning 

 a veil). The sporophytes always remain attached to the parent 

 plant, and finally develop spores asexually in the spore cases. 

 The spores are formed in groups of four, called tetrads, within 

 spore mother cells (Figs. 245, B, s; 258,5). These asexual 



