AZOLLA AND SALVINIA. 



539 



be found in a phaenogamous ovulum, in connection with a 

 plurality of embryo sacs, in which case the similarity will be 

 mainly increased. 



If the comparison is drawn between the organs of Azolla 

 and the ovula of certain Gymnospermous plants at a later 

 particular 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 pistilligerous 

 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 ex- 

 teriorly ; 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 ap- 

 pearances as closely resemble the above as is compatible with 

 the difference in the organs themselves. The supposed fecun- 

 dating matter has appeared, at least after it has come in con- 

 tact with the female organ, to be much the same. 



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



+ Such are the appearances that have been presented to me by ex- 

 amination 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 fecundation. — Linn. Trans, xvii. p. 466-67. 



