532 Sykes and Stiles.—The Cones of the Genus Selaginella. 
(ii) The origin and development of the sporangium. The chief contrast 
between Selaginella and Lycopodinm is in the development of the sporangia, 
which arise from stem tissue in the former, and generally from leaf tissue in 
the latter. At present we are very much in the dark as to the meaning of 
this feature. In Miadesmia 1 the position of the sporangium appears to 
indicate that it was there developed from leaf tissue. Perhaps in Selaginella 
the sporangium has never been taken up on to the leaf, or it may be 
that both here and in Lycopodinm Selago the development of that portion of 
the sporophyll which intervenes between the sporangium and the axis has 
been dropped out and the sporangium has become reinserted on the stem. 2 
At present such suggestions are mere conjectures. 
(iii) The air cavity. The air cavity recorded in the projecting base of 
the sporophyll of S. helvetica , 5 . flahellata , S. caulesce/is , &c., is of some 
interest; it forcibly recalls the mucilage cavity in the genus Lycopodinm , and 
the parichnos of fossil genera. 3 
(iv) It is perhaps also worth mentioning the lignified cells found in the 
stalk of the sporangium of 5 . helvetica and other species. They are, how¬ 
ever, hardly comparable with those occurring in the genus Lycopodinm, 4 
since their walls, unlike the lignified walls of the cells in the sporangium 
stalk in species of that genus, have no pits that are visible under the magni¬ 
fications which we have employed. The lignified walls in both genera stain 
with iodine green and methyl violet. 
(v) The tangential elongation of the microsporangium in 6 *. pnmila , 
vS. helvetica , and .S. spinosa recalls the saddle-shaped sporangium of so many 
of the Lycopods, 5 while the rounded microsporangia of the other forms 
is more like the sporangium of Bothrodendronp Miadesmia? &c. It appears 
probable that the shape of the sporangium is a character largely dependent 
on the relations between the sporophylls and the adaptations for the dis¬ 
persal of the spores, and is not one which can be relied on for comparative 
purposes. 
B. A tendency towards reduction in the number of megaspores in the 
sporangium appears to be prevalent in the genus Selaginella , and is found 
in such widely separated species as 5 . rupestris , 5 . flabellata , and 5. apus. 
This may possibly represent a survival from Palaeozoic times, when it was 
very highly expressed in such forms as Miadesmia. 
1 Benson, M., T908 (1), p. 420. 
2 Sykes, M. G., NewPhyt., 1908; and Ann. of Bot., 1908. 
3 Hill, T. G., 1906, p. 270. 4 Sykes, M. G., 1908 (2). 
5 Sykes, M. G., 1908 (2); Benson, M., 1908 (2), p. 145. 6 Watson, D. M. S., 1908. 
7 Benson, M., 190S (2), pp. 420, 421. 
