GENERAL REMARKS. 



261 



In Azolla the diformity is extreme, it would not be capable 

 of identification, but for the large yellow sac, which is obvi- 

 ously a form of the spore, as pointed out by the trilineal 

 apex. The ternary division of the frondose lobes, suggests 

 the idea of their being metamorphosed spores. And there will 

 be little difficulty in adopting this, if the spores, or small yellow 

 sacs of the pedicellate bodies, are not limited to 4 to each pa- 

 rent cell. This would be an analogy with Mimoseous pollen. 



AZOLLA. 



4. Examination of the middle stage of development of the 

 monogongylus body of Salvinia, shews satisfactorily that the 

 yellow sac is a preponderating spore, so much so, that all the 

 rest are abortive, this is plain. 



It satisfactorily shews that the same is the case in Azolla, 

 the only difference being, that the other sporules do not en- 

 tirely so abort, but that a definite number assume an unusual 

 structure, not dissimilar to those changes in the contents of 

 the normal capsules. 



The great size of the germinating spore, shews that the 

 larger sporules of Isoetes and Psilotum, are to be considered 

 the germinators ? 



Appearances are in favour of the spores of the other organs 

 being abortive ?, they are empty, at least until they are quite 

 enclosed in the cellular masses ; they are not incrusted ; they 

 are like the certainly abortive ones of the oblong body of Sal- 

 vinia, only yellow. 



An evident tendency to Azolla, occurs in Salvinia, as shewn 

 by the greater number of peripherial cells in the upper half of 

 the body.* 



* Points for consideration. Original difference in the nucleus of the 

 ovulum, on which the number of protuberances depends ? The time of 

 first change. 



The situation of the two in Azolla, the gongylus is always (?) under- 

 neath, when associated with a normal capsule. 



