OF FERNS FROM THEIR SPORES. 127 



in the embryo-sac. The succeeding stages of growth of this new cellular body, the embryo, 

 consist of a gradual multiplication of the cells by division, and expansion of the new struc- 

 ture, until at length the rudiments of a radicle and the first leaf become visible as projec- 

 tions from the surface, resulting from the more rapid increase of the cells in the situation 

 where they are found (figs. 76-79). 



In the ulterior development of the embryo the radicle appears to be arrested in its deve- 

 lopment, and to remain as a cellular mass (fig. 80 a) within the cavity of the prothallium, 

 until it disappears with the latter by decay. The first leaf unfolds upwards and forwards 

 (fig. 80 b) towards the notch of the prothallium, and the first adventitious root (fig. 80 c) 

 breaks through at the base of this towards the posterior border of the prothallium, exhi- 

 biting a coleorhize like that of the Monocotyledons. The second leaf arises near the axil 

 of the first, one-third of the circumference of the nascent stem to the side ; the third leaf 

 arises one-third to the side of the second, so that the three leaves form a circle, in which 

 they stand at equal distances, and the fourth leaf arises over the first (Oymnogramma 

 chrysophylla ?). They are of very simple structure, consisting of cellular plates with twice- 

 forked rudimentary nervures, and they are accompanied by very elegant ramenta at the 

 bases of the little petioles (figs. 81-83). * 



I have not followed the development beyond the formation of the fourth leaf (fig. 83), 



by which epoch the prothallium has generally decayed away from the base of the young 



stem. 



V. Criticism of previous Observations. 



The first account of any of the peculiar structures above described was published in 

 1844 by Nageli*, in a memoir entitled " Moving Spiral Filaments (spermatic filaments) in 

 Ferns," wherein he announced the existence of the bodies now called antheridia, but mis- 

 taking the archegonia for modified forms of the antheridia, he was led away from a minute 

 investigation of them. If he had followed the development of the prothallia further, he 

 would have detected the relations of the nascent embryo, which would probably have put 

 him on the right track. As it was, the remarkable discovery of the moving spiral fila- 

 ments, or spermatozoids, occupied all his attention, and caused him to fall into error in 

 certain important respects ; for example, in fig. 11 of his plate, he has represented what 

 is undoubtedly an archegonium, filled with cellules {sperm-cells), which, he states, emerged 

 from it as from the antheridia : this is undoubtedly incorrect. 



With regard to the spermatozoids his description is imperfect, the only indication of the 

 existence of cilia being a statement that he occasionally saw a long filiform appendage, 

 like that represented by Meyen in the spermatozoids of Chara. On the other hand, the 

 mathematical definition of the movements of the spermatozoids is surely misplaced, since 

 nothing can be more arbitrary or irregular than their course. 



However, whatever be the faults of observation, it is certain that it is to the keenly 

 inquiring spirit of this author that we owe the first step of the investigations which have 

 thrown so much light upon the reproduction of the higher Cryptogamia. 



Nageli's observations remained without confirmation or criticism until the publication 

 * Zeitschrift fur wiss. Botanik. Heft i. 168. Zurich, 1844. 



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