454 Mr. A. Henfrey on the Reproduction of the 



form suspensors, bearing embryos which they carry down into the 

 substance of the lower part of the ovule. In Selaginella the 

 germ-cell of the archegonium grows down into a suspensor, and 

 developes the embryo in the cellular tissue inside the cavity of 

 the spore quite below the prothallium. 



The principal difference in Salvinia seems to be the absence 

 of the suspensor, the embryo originating in the substance of the 

 prothallium, which has several archegonia. Pilularia differs again 

 from Salvinia in having only one archegonium. 



In these tribes of the Cryptogamia, the stage of development in 

 which the prothallia with the sexual organs appear — after the 

 spores have become entirely separated from the parent, thus 

 constituting separate entities, — is comparatively brief; it is a 

 transitory stage of the development of the forms representing 

 the species ; the prothallium being moreover very inconspicuous 

 and almost wholly inclosed in the spore-coat. 



We find a very great difference in the Ferns and Equisetacea?, 

 which may be grouped together. Here the representatives of the 

 pollen-grains, the small spores, disappear, or at least only one 

 kind of spore is formed ; from this is developed a prothallium, 

 which becomes a more important and conspicuous structure. 

 No longer hidden in the spore-coat, it grows out into a Mar- 

 chantia-like frond, well-provided with chlorophyll, having root- 

 fibrils, and lasting, especially in the Equisetace?e, many months. 

 This structure produces not only archegonia, but also antheridia, 

 emitting spermatozoids. Hence the prothallium here combines 

 the analogy to the endospermous tissue of the embryo-sac of the 

 Gymnosperms with an analogy to the pollen-mass. Hence while 

 the stems and fronds of the Ferns, and the shafts of the Equiseta 

 are represented by the stem and leaves of the Gymnosperms, the 

 fertile fronds and spikes of the former find their analogues in 

 the cones of the latter. The spike of the Equisetum closely re- 

 sembles the cones of some Conifers ; the fertile fronds of the 

 Ferns, especially in certain cases, approach to the cones of the 

 Cycads, with their numerous ovules on abundant anthers upon 

 each scale or leaf. The male and female influence lie as yet 

 combined in the spores of the Ferns and Equiseta, to become 

 disentangled during the development of the prothallium ; the 

 sexual influences are already separated in the cones of the Coni- 

 fers and Cycads, where the uniform spore of the Filicoids is re- 

 presented respectively by the pollen-mass or the embryo-sac of 

 the ovule. 



The Mosses present another kind of disintegration of the spe- 

 cific form, if it may be so termed, into distinct existences, the 

 conditions of the prothallium and the spore-bearing generation 

 being reversed here; the former being the more permanent, 



