ON THE HIGHER CRYPTOGAMOUS PLANTS. 115 



by peculiar thickenings of the tissue to protect the pro-embryo during germi- 

 nation. The contents of the nucleus were stated to resemble those of the 

 cavity of the spores of Selaginella. 



In these contents, which become dense and mucilaginous, a free cell is de- 

 veloped near the upper part of the cavity ; this is the rudiment of the embryo, 

 and by cell-multiplication becomes a cellular mass, which soon begins to ex- 

 hibit growth in two directions, producing the first leaf and the first rootlet, 

 projecting from a lateral cellular mass, which the author calls the " reservoir 

 of nutriment." The embryo then breaks through the coats ; the first leaf 

 above and the first root below, the coats remaining attached over the central 

 mass of the embryo. The subsequent changes need not be mentioned here, 

 further than to state that the leaves succeed each other alternately, and are 

 not opposite as in the Lycopodiaceae ; moreover no internodes are developed 

 between them, so that the stem is represented by a flat rhizome, like the base 

 of the bulb of many Monocotyledons. 



In the paper by Dr. Mettenius*, already alluded to, we find some very im- 

 portant modifications of and additions to this history of development of the 

 spores of Isoetes, bringing them into more immediate relation with the other 

 vascular Cryptogams. 



This author describes the spore-cell as a thick structure composed of seve- 

 ral layers ; in some cases he counted four. It completely invests the pro- 

 embryo, which is a globular cellular body filling the spore-cell. Among 

 the cells of the outermost layer of the pro-embryo (which layer forms the 

 nucleus of Dr. Miiller), on the upper part, are produced the ovules, fewer in 

 number than in Selaginella, arranged in three rows converging upon the 

 summit of the spore, these rows corresponding to the slits between the lobes 

 of the outer coat of the spore. The four superficial cells of the ovules (which 

 are evidently the peculiar groups mentioned by Miiller and previously no- 

 ticed by Valentine f) grow much in the. same way as in the Rhizocarpeae 

 and in Selaginella, into short papillae. The embryo is developed in the sub- 

 stance of the pro-embryo, displacing and destroying its cells, and a globular 

 portion (corresponding to the " reservoir of nutrition" of Miiller) remains 

 within the spore after the first leaf and rootlet have made their way out. 

 This body is the analogue of that portion of the embryo oi Selaginella which 

 penetrates into the cavity of the spore, and to the end of the first axis in the 

 Rhizocarpeae. 



The most important point, however, of Dr. Mettenius's researches relates 

 to the phaenomenon exhibited by the small spores. In the water in which 

 the spores were sown he observed moving spiral filaments resembling those 

 of the Ferns. He was not able to trace all the stages of development of these 

 spiral filaments from the small spores, but he obtained nearly all the evidences 

 relating to their origin which Nageli has done in reference to the similar 

 organs in the Pilularia%. In the small spores minute vesicles are produced 

 of varying size and number, seen through the outer coat. The inner coat or 

 spore-cell breaks through the outer coat either in the middle or at both ends 

 at the projecting ridges, by which they are originally in contact with the other 

 spore-cells. Its contents are expelled, as is proved by finding numerous 

 empty membranes. The expelled vesicles are met with in considerable num- 

 ber in the water, and contain one large or several small granules, and in 

 them the spiral filaments are apparently produced ; but the actual course of 

 development was not observed. In one case a spiral filament was seen halt 



* Beitrage zur Botanik. Heidelberg, 1850. t Linnsean Transactions, vol. xvii. 



t Zeitschrift fur Wiss. Botanik, Heft 3. Zurich, 1846. 



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