248 On Azolla and Salvinia. 



between pollen and spores, it is to be borne in mind, that 

 whereas pollen is the result of a simple separation consti- 

 tuting a primary and independent process ; in Musci, 

 Hepaticae, Salvinidae, the spores, otherwise so similar to 

 pollen, are the result of a secondary process, dependent 

 on a primary one which appears to be remarkably analogous* 

 to phanerogamic fecundation. 



Among the peculiarities of the developments of the spores 

 I may mention the comparative obscurity of the parent 

 cells, which in all other similar plants examined by me have 

 been obvious enough, especially in Isoetes and Marsilea, 

 the spores being visible enough in the parent cells, within 

 which their outer coat even becomes developed. In these 

 plants however it is so obscure, and the separation takes 

 place at such an early period, and apparently so rapidly, 

 that for some time I was almost reduced to consider 

 the trifacial cells, as parent cells, each containing S spores 

 in a state of extreme contiguity. In no instance did I 

 observe the parent cell of the central sac, (subsequently 

 the yellow sac,) or its companions. And although I have 

 examined many instances, yet in none did I find the usual 

 relations continued, that might have been expected as long as 

 the trifacial cells remained imbedded in grume. So much 

 so, that for a second time I was almost reduced to look on 

 them as parent cells. 



* The identity of the spores of Acotyledonous and the pollen of Cotyledonous 

 plants is perhaps strengthened by the curious resemblance of the fructification 

 of Equisetum to the male apparatus of Cycadeae ; in which also the pistillary 

 apparatus, in this view to be looked on as a sort of nidus, is of great simplicity. 



Mr. Valentine's account was read before the Linn. Socy. in 1833, and appeared 

 in 1837. M. Schleiden's was extracted in the Lond. Edin. Phil. Mag. from 

 Weigmann's Archiv. fiir Zoologie, pt. iv. 1837. The similarity between the obser- 

 vations of the two is remarkable, and gives the hypothesis great importance. M« 

 Schleiden has however an advantage in my opinion from considering the embryo 

 to be a growth of the ends of the pollen-tubes, and from acknowledging the 

 difficulties presented by Musci, Hepaticae and Rhizocarpeae. 



