208 



MORPHOLOGY. 



tinous envelope, while their external pollen-membrane is tough 

 and studded with papillae. 



In Salvinia the seed-buds and anthers are in distinct fruits. On 

 each spike is to be found an upper fruit, somewhat removed from 

 the rest which are crowded together, and this alone contains seed- 

 buds. The fruits are vertically furrowed, like a melon, and in 

 each projecting ridge runs an air-passage, again divided by a hori- 

 zontal septum ; otherwise, the cellular tissue surrounding the cavity 

 has delicate walls, and becomes gradually dissolved without any 

 regular dehiscence of the fruit. Into the cavity of the fruit pro- 

 jects, from the base to about half-way up, a central columella, 

 spherically expanded above, which bears upon its globular end in 

 one kind of fruit the seed-sacs, in the other the anthers. The 

 peduncle of the ovate seed-sacs is composed of several collateral 

 rows of cells. The sac (a single layer of cells) encloses the seed- 

 bud (the nucleus of which lies as in Pilularia), and separates with 

 the seed-bud from the peduncle. The peduncle of the globular 

 anthers consists of a single row of cells. The external pollen- 

 membrane is very thin and smooth. 



Azolla is not, I believe, nearly sufficiently investigated ; what 

 has hitherto been found allows of no reference to the analogous 

 organs in the Rhizocarpece above mentioned. I myself have not 

 been able to examine any yet, and I refer to Robert Brown* and 

 Meyenf for more special details. 



For the illustration I give the analysis of the reproductive organs of 

 Salvinia natans (figs. 151, 152.). The course of development of the 



151 



152 



I) 



* Verm. Schrift. vol. iii. p. 22., and vol. i. p. 162. ; and the Atlas of Flinders's Voy- 

 age, which contain Ferd. Bauer's beautiful illustrations. 



f Acta Ac. C. L. N. C. vol. xviii. part i. p. 508. 



131 Salvinia natans. Portion of a flowering plant, with two leaves, a branch dipping 

 down iti the water, from which a tuft of rootlets springs, and which bears at the lower 

 part capsules with pollen-sacs (anthers), and above, somewhat removed from the rest, a 

 solitary capsule (ff), which bears seed-sacs. 



133 Salvinia natans. A, Pollen-sac. B t Poll en -granules ; two compressed, with their 



