THE HOMOSPOROUS LEPTOSPORANGIATJE 



367 



hedral, and contain no chlorophyll. When the ripe spores are 

 sown, after a few days the oil-drops become much smaller but 

 more numerous, and the first chloroplasts become evident. 

 The latter increase in number and size, and small starch grains 

 are developed. The exospore is ruptured in from tw^o to three 

 weeks from the time the spore is sown, and the spore contents 

 surrounded by the intine project through the opening. The 

 first wall usually separates the first rhizoid, which, like that of 

 Osmiinda, often contains a good deal of chlorophyll, from the 

 larger prothallial cell. As a rule the development of the pro- 

 thaliium corresponds closely to that of the Polypodiacese, but 



Fig. 209. — Gleichenia pectinata. A, Ripe archegonium; B, nearly ripe antheridium ; i, 

 surface view; 2, optical section; C, apex of open antheridium, showing the method 

 of dehiscence; D, section of very young antheridium. All figures X about 250. 



it may have a midrib like that of Osmunda. The growth is 

 normally from a two-sided apical cell, which is replaced later 

 by marginal initials. A point of resemblance to Osmunda is 

 the abundant production of adventitious shoots, which are 

 formed in numbers upon the margin or from the ventral sur- 

 face, and may develop into perfectly normal prothallia. 



Rauwenhofif's account of the sexual organs is not as com- 

 plete as might be wished, but is sufficient to show some inter- 

 esting points of resemblance to the Osmundacese. The first wall 

 in the antheridium cuts off a basal cell, and the next wall is 

 somewhat like the funnel-shaped wall in the Polypodiaceae. 



