AZOLLA AND SALVINIA. 



545 



posed female, as well as in that of the acknowleged spores of 

 some other acotyledonous families, in which nevertheless the 

 evidence in favour of sexes is acknowledged to be the most 

 complete. The same argument, so extended as to include 

 both kinds of bodies, may be advanced. In this case they 

 will enter the hypothesis of Mr. Valentine,* which must, 

 however, to be consistent with analogy suppose the absence of 

 sexes in all Acotyledonous plants. This I think difficult 

 to do, and while I fully agree in the remarkable similarity 

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

 whereas pollen is the resuk of a simple separation consti- 

 tuting a primary and independent process ; in Musci, 

 Hepapticae, Salvinidse, 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 development 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 how- 

 ever it is so obscure, and the separation takes place at such 



* Linn. Trans, xvii. p, 480, 481 ; xvii. p. 502. 



t The identity of the spores of Acotyledonous and the pollen of Coty- 

 ledonous plants is perhaps strengthened by the curious resemblance of 

 the fructification of Equisetum to the male apparatus of CycadeEe; 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. fur Zoologie, pt. iv. 1837 

 The similarity between the observations 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, Hepaticse and Rhizocarpese. 



3 v 



