242 On Azolla and Salvinia. 



If the comparison is drawn between the organs of Azolla 

 and the ovula of certain Gymnospermous plants at a later par- 

 ticular period, we find the resemblance to be increased by 

 the occupation of that part of the interior of the ovulum, (or 

 body,) between the foramen and the apex of the nucleus, by 

 a number of grains derived from without.* This circum- 

 stance in Gymnospermous plants is explainable by the ex- 

 ternal relations of the ovula being so much more direct 

 than in Angiospermous plants. And the same may be said 

 of Azolla (and Salvinia) if they are compared with pistillige- 

 rous Acotyledones. 



I have here set aside the nature of the grains found in the 

 ovulum of Azolla for the sake of exactness, but there are pre- 

 sumptive evidences that the analogy may be extended to the 

 functions of the grains themselves. 



The evidences in favour of fecundation are, I think, as 

 strong as they are in Musci and Hepaticae, in which I de- 

 rive them from the breaking up of the tissue terminating and 

 closing the style (subsequently to the application of a parti- 

 cular matter,) whereby the style becomes a canal opening 

 exteriorly; from the browning observable in the orifice of 

 this canal extending downwards until it reaches the cavity 

 of the ovarium, and from the corresponding enlargement of 

 the cell (ovulum) existing in that cavity.f In Salvinia the 

 appearances as closely resemble the above as is compatible 

 with the difference in the organs themselves. The supposed 

 fecundating matter has appeared, at least after it has come 

 in contact with the female organ, to be much the same. 



In Azolla the evidence consists in the derivation of the 

 grains from without, on the browning of the foramen after 



* For instance Cycas ; I have drawings illustrating this, made in 1835. 



f $uch are the appearances that have been presented to me by examination of 

 Phascum and Funaria; by Mr. Valentine however neither the opening of the apex 

 of the style or the browning is supposed to be in any way connected with fecunda- 

 tion. — Linn. Trans, xvii. p. 466-67. 



