ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
643 
development are evidence of the close relationship of the genera of Rhizo- 
carpeae with one another, and that both in the divisions of the prothallium 
and in the structure of the antherid itself Between the two genera of 
Marsileaceae the resemblance is much closer than between the two genera 
of Salviniaceae ; and the facts appear to indicate that the former is the 
lower and older family. 
In Salvinia the prothallium is from the first dorsiventral. It first of 
all divides by two septa, of which one is nearly horizontal, and the other 
oblique, into three segments. Of these the lowest, which is somewhat 
larger than the other two together, undergoes no further alteration 
except the cutting off of a very small lenticular cell at its base. The 
middle and upper segment each divide into three by two successive, 
nearly parallel septa. In each segment the central cell is the antherid, 
the two which bound it on each side are barren. The mature prothallium 
therefore consists of eight cells, of which six are barren, the other two 
being two antherids completely separated from one another. The 
antherid finally breaks up into four antherozoid mother-cells. 
In Azolla the first processes of division correspond to those in 
Salvinia. The prothallium divides into three segments, and from the 
lowest of these a small lenticular cell is cut off. But the uppermost 
segment undergoes no further division, while the central segment divides 
by successive divisions into a large central and four sterile cells. The 
mature prothallium consists of a single antherid and seven barren cells. 
The antherid breaks up into eight antherozoid mother-cells. 
In Marsilea and Pilularia the processes are far more difficult to 
follow in consequence of the hard dark epispore. The prothallium of 
Marsilea is nearly spherical, and its dorsiventrality greatly obscured. 
The mature prothallium consists of eight sterile cells, and two antherids 
completely separated from one another; in each antherid 16 antherozoid 
mother-cells are produced. In Pilularia the processes appear to be 
similar as far as they can be followed out. 
A comparison with the development of the prothallium in Filicincae, 
especially in the Hymenophyllacese, leads the author to the conclusion 
that the small cell which is cut off from the lowermost primary segment 
in the Rhizocarpese is a rudimentary rhizoid. 
Musclnese. 
Braithwaite’s British Moss Flora. — Part xiv. of this work continues 
the description of the Bryaceae. It deals with the genera Polilia (twelve 
species), Epipterygium (one species), Plagiobryum (two species), and 
commences the large genus Bryum , which is divided into three sections 
— Sclerodontium (two species), Cladodium (nine species), and Eubryum 
(twenty-four species). The part is illustrated by six excellent plates. 
Algae. 
Cultivation of Marine Algse.* — Dr. F. Noll explains the contri- 
vances by which he has been successful in growing sea-weeds in aquaria. 
Besides attention to the composition of the water, constant change is 
necessary, in order that the plant may be supplied with a sufficient 
* Flora, Ixxv. (1892) pp. 281-301. Cf. this Journal, ante, p. 396. 
*2x2 
