228 



PLANT MORPHOLOGY 



below the surface of the ground and requires the greatest number of years 

 to reach maturit^^ 



It is an interesting fact that only species with a green aerial prothal- 

 lium have a sporophyte that passes through a Phylloglossum-\ike stage in 

 its early development. The prothalliura of such species doubtless repre- 

 sents a primitive type from which the colorless subterranean prothallia 

 have been derived. Their development may have been caused by 

 delayed germination of the spores, resulting in their burial in the soil. 



Fig. 184. Antheridial development in Lycopodiiim clavatum, X 150. A, to the right, a 

 young antheridium after first division of initial cell; to the left, a much older stage; B, 

 vertical division of primary wall cell and primary spermatogenous cell; C, further division 

 of spermatogenous cells; D, nearly mature antheridium, showing wall and spermatogenous 

 tissue; E, two sperms, X625. (After Bruchmann.) 



In fact, in some species, a spore will produce a green prothallium if it 

 germinates on the surface of the ground and a colorless one if it germinates 

 below the surface. 



Both kinds of sex organs are borne in rather large numbers on the same 

 gametophyte. The antheridia are either completely embedded or 

 slightly projecting. They are globular, have a sterile jacket consisting of 

 a single layer of cells, and produce many small, slightly curved, biciliate 

 sperms (Fig. 184). In development, a superficial initial divides by a 

 periclinal wall to form an outer 'primary wall cell and an inner primary 

 spermatogenous cell. The former gives rise to the sterile jacket, the latter 

 to the mass of spermatogenous tissue. 



The archegonia are also embedded in the prothallium, only the neck 

 protruding (Fig. 185). The initial is superficial and gives rise, by a peri- 

 clinal division, to an outer primary neck cell and an inner cell that again 

 divides to form the central cell and hasal cell (Fig. 185A, B). The central 

 cell gives rise to two cells, the outer one being the primary neck canal cell 



