VII PTERIDOPHYTA—FILICINEAl—OPHIOGLOSSACEJE 235 



with numerous oil-drops, and a central lar,e^e and distinct 

 nucleus. The exospore is colcjurless, and upon the outside 

 presents a pitted appearance in Ophioglossuni, and irrej:^u]ar 

 small tuhercles in Botrycliiiini. The jicrinium or epis])ore is not 

 clearly distinguishable from the exospore. in both cases 

 chlorophyll is absent in the ripe spore. The first sign of ger- 

 mination is the absorption of water and splitting of the exospore 

 along the three radiating lines en the ventral surface of the 

 spore. The spore enlarges considerably before any divisions 

 occur, but remains globular in form, and no 

 chlorophyll can be detected. In this con- 

 dition, which was observed within two 

 weeks after the spores were sown in Ophio- 

 glossnm, it may remain for several months 

 unchanged. The first division wall is 

 usually at right angles to the axis of the 

 spore, and divides it into two nearly equal 

 cells, of which the lower has more of the 

 granular contents than the upper one. The 

 endospore is noticeably thickened where it 

 protrudes through the ruptured exospore. 

 The next wall, in all cases observed, is at 

 right angles to the first, and always in the 

 lower cell, which it divides into equal parts 

 (Figs. 124, 125). In Botrychmm at this 

 stage a few large chloroplasts were seen in 

 both upper and lower cells, but Ophioglos- 

 sum showed no positive evidence of 

 chlorophyll, although it seemed sometimes 

 as if a faint trace of chlorophyll could be 

 detected. As growth proceeds, the oil 

 partially disappears, and the cells become 

 much more transparent than at first. 



Lang (4) found the prothallia of Ophioglossum pendulum 

 burled in the humus collected about masses of epiphx-tic ferns 

 among which the sporophytes of the Ophioglossum were grow- 

 ing. The youngest ones discovered were nearly circular in out- 

 line, the older specimens more or less branched (Fig. 125, C). 

 The branches are cylindrical and grow from a single initial cell 

 which has the form of a four-sided pyramid. The lower half 

 of the prothallium is infested by an endophytic fungus, while 



Fig. 124. — Germinating 

 spore of Ophioglossum 



{Ophio derma) pendu- 

 lum. A, Surface view; 



B. optical section, 



X600. 



