124 



THE MARATTIALES 



THE PROTHALLIUM OF DAN^A. 



In July, 1908, the prothallia of three species oiDancea were collected in Jamaica. 

 As the genus Dancea has received comparatively little attention, especially as regards 

 the gametophyte, it seemed very desirable to secure as complete a series of the pro- 

 thallia and young sporophytes as could be done, and to this end the trip was made 

 to the West Indies. The genus Dancea is confined to the American tropics and 

 comprises, according to Christensen, 26 species of extremely characteristic ferns. 

 The type is evidently an old one, as some of the fossil Marattiaceae are closely allied 

 to the living genus Dancea and may possibly be referred to it. The only account of 

 the prothallium hitherto published, so far as I am aware, is the paper of Brebner 

 (Brebner 2) on D. stmpltcifolta, a species from British Guiana. 



In 1897 I collected a small number of specimens of prothallia oi Dancea, prob- 

 ably D. jenmani, and in the summer of 1908 the same locality was visited, as well 

 as some others in the same district, and material of three species was secured. These 



Ku;. 91. 



A. Three gametophytes of Danxa jenmani Underwood. Xz. 



B. Three young gametophytes of D.jamaicensh Underwood. X4. 



C. Four large gametophytes of D.jamaicensis. X2. 

 C, I, shows four groups of archegonia, ? . 



collections were all made in the vicinity of Cinchona, a mountain station at an eleva- 

 tion of about 5,000 feet. As I have found in collecting other Marattiaceze, the most 

 favorable collecting ground for the prothallia is upon moist, clayey banks where the 

 fruiting plants are growing. In the shady crevices in such positions a careful search 

 will usually be rewarded by the discovery of numerous young plants, and with these 

 there are often associated prothallia in various stages of development. Brebner 

 described the prothallia of D. stmplicifolia as being nearly circular in outline, but 

 very few of the prothallia of the species collected by me showed this form; but they 

 were usually decidedly elongated, sometimes very strongly so, and were, as a rule, 

 very much larger than the specimens of D. simpUcifoUa described by Brebner. 



The three species collected by me were D. jamaicensis Underwood, D. jenmani 

 Underwood, and D. elliptica Smith. In all three species the larger prothallia are 

 usually decidedly elongated and very irregular in outline, often showing conspicu- 

 ous leaf-hke marginal lobes, like those occurring in the prothallia oWsmundaznd 

 Gleichenia. 



