1 62 Campbell. — On the Development of 
by the indusium, and the origin of the latter from so near the 
base of the sporangium, at once suggest the possibility of 
a homology between the indusium and the first integument of 
the ovule. Prantl 1 has advanced the view that an ovule might 
be regarded as a monangic sorus, and the integument as 
homologous with the indusium. So far as I can find, Azolla 
has not been considered in the arguments for and against this 
view, but it certainly supports strongly the view held by 
Prantl 2 . Of course this does not imply a direct relationship 
between Azolla and the Spermaphytes, as the sporangia 
themselves are widely different, Azolla being typically lepto- 
sporangiate, while the Spermaphytes are eusporangiate. Never- 
theless, in view of all the facts bearing on the matter, it hardly 
seems necessary to regard the ovular integument as an entirely 
new structure, without any equivalent among Pteridophytes. 
The ripe female sporocarp is about i*5 mm. x i mm. in 
size, and strongly pointed at the top. Its outer cells become 
hardened, and those of the upper half very dark-coloured and 
lignified, so that after the lower part decays, these upper, dark- 
coloured cells remain as a little cap that covers the spore 
until it is thrown aside by the growth of the embryo. The 
inner cells of the wall remain thin, and become very much 
compressed by the growth of the sporangium which finally 
fills the sporocarp completely. The wall of the sporangium 
does not, however, as stated by Strasburger 3 , become 
absorbed. On the contrary, it can be plainly seen in sections 
of the full-grown sporocarp (see PI. VIII, Fig. 38), but the cells 
are much flattened, and unless carefully examined might be 
taken for the inner layer of the indusium, which is compressed 
so as to be almost obliterated. 
A longitudinal section of the full-grown sporocarp (Fig. 35) 
shows that the spore 4 with its curious appendages fills the 
1 Untersuchungen zur Morphologie der Gefasskryptogamen : Die Schizaeaceen, 
P- 154 * 
2 Since the above was written, I find that Eichier has called attention to the 
resemblance between the sorus of Azolla and an ovule : see Engler and Prantl, 
Die nat. Pflanzenfam. II. Theil, i. Abth. p. 16. 3 loc. cit. p. 71. 
4 Sometimes two spores are found in one sporangium. 
