219 Howe and Underwood : The Genus Riella 



barium of the New York Botanical Garden. The plants are said 

 by Professor Earle to have been found in a pool headed by a small 

 waterfall, forming mats on rocks and stones which were covered 

 by 10-60 cm. of water in the dry season. The same species was 

 collected by Schott in 1855, his specimen originating from 

 " Limpia, near its head, Western Texas." His plants, though 

 otherwise agreeing perfectly with those of the more recent col- 

 lection, are considerably smaller and are mostly unbranched. A 

 Riella (in herb. A. W. Evans) was collected by Mr. De Alton 

 Saunders at Brookings, South Dakota, in 1898. The material is 

 scanty and the sporogonia are so immature that the spore-char- 

 acters cannot be determined. The involucres and scales are 

 similar to those of R. Americana and it is quite probable that the 

 species is the same. This South Dakota specimen marks the 

 northern limit in the known distribution of the genus. 



Riella Americana is easily distinguished from any of the species 

 hitherto known. Its nearest ally is probably Riella Battandieri f. 

 Gallica, of southern France, which differs in being monoicous," 

 in the narrower wing, the smaller spores, with shorter non-capi- 

 tate spines, etc. Gemmae have not before, to our knowledge, been 

 definitely described in any species of Riella, though Goebel (Flora, 

 77 : 105. 1893) in figuring three young stages of Riella Battan- 

 dieri (?) remarks in a footnote that one of them sprang from a 

 " Zellkorper " while the others came from " Zellfaden." By anal- 

 ogy with what we have observed in Riella Americana, it seems very 

 probable that his plant from the " Zellkorper " came from a brood- 

 body of some kind, while those from the " Zellfaden " were de- 

 rived from spores. The young plants oi Riella Cossoniana, repre- 

 sented by Trabut in his figures i and 2 (/. r.),also, with little doubt, 

 originated from gemmae. The gemmiform appendages figured by 

 Trabut on the axis of his R. Gallica are of a more doubtful nature. 

 These were not found by Corbiere in his recent studies of what he 

 believes to be the same species ; possibly they were designed to 

 represent remains of old involucres and sporogonia. 



The gemmae of R. Americana originate on the axis as trichomic 

 outgrowths, each of about three cells in a single series (/. 10, 

 11) of which the terminal cell is usually the largest. The two 



* Corbiere, Rev. Bryol. 29: ill, 113. 1902. 



