DEVELOPMENT OF THE OSTRICH FERN. 49 



comes lai'ger and elongated and eoarsely granular in appearance. In some cases ol)- 

 seryed at tliis stage, the nnclens was extraordinarily distinct. The nucleus increases 

 greatly in size, but becomes much less distinct (fig. 25), and careful observation shows 

 the tbrmation of tlie nuclear s])in(lle, but no satisfactory view of the nuclear disc couhl 

 be obtained, although usually there was an evident line separating the two paits of tlu' 

 mother-cell, which at this stage has increased slightly in size and become somewhat oval 

 in form. The two secondary nuclei are formed at the poles of the' luiclear spindle and 

 become, when complete, much like the primary nucleus. They very soon divide again, 

 pi'obably in the same way as the i)rimary nucleus, resulting in the four nuclei of the 

 young sjjores. Although thei'e is a dividing line between the two masses of ])roto])lasm 

 into which the mother-cell first divides, no cell wall seems to be formed; Init after the 

 secoud division is complete, the young spores Ijccome separated by walls. The plam-s 

 of division of the nuclei are at right angles, so that of the four resulting sporc^s, two 

 lie in one plane and two in another. After division is completed, the spores liegin to 

 lose the granular appearance they hitherto exhibited and become more transparent, 

 lliey now separate, l)ut remain sufficiently united to sliow which belong togetliei' 

 and have become almost destitute of graiuilar contents. They ai-e kidney-sha])ed, 

 slightly flattened on one side, but ajipear oval if seen from above. Each is ])rovidi'd 

 Avith a very distinct nucleus, eml)edded in the protoplasm near the wall on the flattened 

 side. The sjjores rapidly increase in size until they are about twice as large as when 

 first formed, this increase being probably due to the using up of the matci'ial derived 

 from the tajjctal cells. Each spore has a distinct wall which is early [)artially diflei-en- 

 tiated into an inner and outer wall. A third coat, brown in color (the exosj)ore), Anally 

 appears and attains considerable thiclaiess. It becomes provided with a series of i-idges 

 or folds (fig. 27), l)ut e\en when young is easily separated from the spoi'e 1)\' slight 

 friction. Before the exospore is formed, very fine granules are seen to ajj]x'ai-, most 

 abundantly in the vicinity of the nucleus. These rapidly enlarge and are seen to undt'r- 

 go division. About the time that the exospore begins to develo[), some of them become 

 tinged with chloro])Iiyll. and c<mtinuing to form rapidly, the spore soon becomes densely 

 crowded with them, so as almost to c(mceal the nucleus and i-ender the wiiole spore 

 almost i)erfectly ojjaque and dark green. The nucleus changes its position, moving 

 toward the center of the s]jore, the exospoi'c reaches its full thickness, and the spore is 

 complete. 



AVhile the spores have been developing, during Avhich time they have grown so as to 

 fill the sporangimn completely, the parietal cells of the sporangium have also undei-gone 

 marked changes. The cells of the annulus, which at first were distinguished fi-om the 

 other cells simply liy their form, begin to project above the level of the others and tlieir 

 division walls become thicker. At this stage (fig. 24) all the ])arietal cells are trans- 

 parent and colorless, and are distinctly nucleated. The cells of the anmilus on one side 

 of the s])orangium are rather more elongated transversely than the others, tliese being 

 very much more strongly marked in four, or sometimes only three, near tlie base of the 

 capsule, forming the stomium, or point at which the capsule ojiens. The division walls 

 are also tliicker in the cells of this sirnctnrc wliicli is specially well dexcloped in ihe fei'ii 

 nndi'r consideration. 



MEMOIHS HOSTON SOC. N'AT. HIST., VOL. IV. 



