358 MOSSES AND FERNS chap. 



the tropics of the whole world. It has very long leaves, which 

 fork repeatedly, and may be proliferous from the growth of buds 

 developed in the axils of the forked pinnae. 



The development of the prothallium has been studied by 

 Rauwenhoff,^ and shows some interesting points in which it is 

 intermediate between the Osmundaceae and the other Leptospor- 

 angiatae. The spores of Gleichenia are usually tetrahedral, 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 two 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 Osinunda, often 

 contains a good deal of chlorophyll, from the larger prothallial 

 cell. As a rule the development of the prothallium corresponds 

 closely to that of the Polypodiaceae, but it may ha.ve a midrib 

 like that of Osinunda. The growth is normally from a two- 

 sided apical cell, which is replaced later by marginal initials. 

 A point of resemblance to Osinunda is the abundant production 

 of adventitious shoots, which are formed in numbers upon the 

 margin or from the ventral surface, and may develop into 

 perfectly normal prothallia. 



Rauwenhoff's account of the sexual organs is not as 

 complete as might be wished, but is sufficient to show some 

 interesting points of resemblance to the Osmundaceae. The 

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

 wall is somewhat like the funnel-shaped wall in the Polypodi- 

 aceae, The dome-shaped wall next formed is here not so 

 marked, being nearly flat.^ No definite cover cell is cut off", 

 but the upper cell appears to divide by a single wall running 

 obliquely over the apex, somewhat as in Osmunda. The 

 divisions in the central cell offer no peculiarities, and the 

 spermatozoids resemble those of other Ferns, The archegonia 

 are formed on the forward part of the midrib, but are not 

 confined to the sides, as in Osinunda. Apparently a basal cell 



^ Rauwenhoff (i). 



- Rauwenhoff's statement that the central cell of the antheridium contains chloro- 

 phyll, to judge from his Fig. 58, which illustrates this, is based upon a pathological 

 case. The absence of chlorophyll from the central cells of the antheridium is a very 

 constant character in all Archegoniates. 



