760 SUMMARY OF CURRENT RESEARCHES RELATING TO 
essential parts of the sporange may be traced to a single superficial cell. 
The tapete is derived from the series of cells immediately surrounding 
the sporogenous tissue. The author regards the whole sporangiophore 
of Psilotum as of foliar nature, the synange being a growth from its upper 
surface. The synange of the Psilotacese is homologous with the “ fertile 
frond ” of the Ophioglossaceae. The relationship is further pointed out 
between Tmesipteris and Lepidodendron. 
Development of Azolla.* — Prof. D. H. Campbell has followed out in 
detail the life-history of Azolla filiculoides. The stem always grows from 
a single apical cell, from which two series of segments are cut off with 
great regularity. The sporocarps or sori always arise from the ventral 
lobe of the first leaf of a branch. The whole of the ventral lobe goes 
to form the sori, the involucre being derived from the whole of the 
dorsal lobe. In all cases only one megasporange is formed, and this 
directly from the apical cell of the sporocarp-rudiment. The divisions 
in the central cell correspond to those in other Leptosporangiates. The 
development of the megasporange bears a remarkable resemblance to 
that of an ovule, the indusium being apparently homologous with the first 
integument of the ovule. The term “ swimming apparatus,” which has 
been applied to the singular episporic appendages of the megaspore, is 
misleading ; they apparently have no such function, the spores always 
sinking in the water. 
The development of the microsporange corresponds in essential points 
to that of the megasporange ; the formation of the massulas and glochids 
is described in detail, as well as the germination of the microspores and 
megaspores. The antherid appears to consist of two cells only. Azolla 
differs from the other Hydropterideae in the lower of the two nuclei 
which result from the division of the primary nucleus of the megaspore 
being equal in size to the nucleus of the prothallium mother-cell, and 
undergoing repeated division. A nucleated protojdasm or “ endosperm ” 
is thus formed, and it is evidently concerned in the elaboration of the 
reserve food-material in the spore ; the process resembles that in Sola - 
ginella. If the archegone first formed is fertilized, no others are 
formed, but when this is not the case, a number of secondary archegones 
are produced. The development of the archegone closely corresponds 
to that in Salvinia. 
The general conclusion arrived at by the author is that the nearest 
ally to Azolla is unquestionably Salvinia , though there are important 
differences. From the Marsileaceae the divergence is still greater. The 
two families of the Hydropterideae probably represent the ends of two 
different lines of development, the Salviniaceae having been derived from 
the lower members of the Leptosporangiate series, near the Hymeno- 
phyllaceae, the Marsileaceae from forms more resembling the Poly- 
podiaceae. 
Colonies of Anabsena Azollse were invariably found in the large 
cavity of the dorsal lobe of the leaf. Before the megasporange becomes 
enclosed in the indusium, the Anabsena filaments creep into it, and form 
a mass filling up all the space between the top of the sporange and the 
opening of the sporocarp. 
* Ann. Bot., vii. (1893) pp. 155-88 (3 pis.). Cf. this Journal, 1892, p. 825. 
