316 LYCOPODIALES 
may vary in different species though the numerical relation of one to each 
subtending leaf is strictly maintained. There is considerable divergence 
of opinion as to the details of its early development, which not 
improbably arises in part from want of exact uniformity in different 
species, partly from difficulty of observation, owing to the small size of 
the cells in young stages! It has been seen above that S. sfzmulosa is 
among the least differentiated species, as 
regards external form, and on that account 
it deserves special attention. The de- 
scription here given will be based on that 
species. According to Goebel the whole 
sporogenous tissue, as seen in the radial 
section in S. spinwlosa, is referable in 
origin to a single archesporial cell, which 
is, however, one only of several forming 
a tangential series. I do not deny that 
this may sometimes be the case; but in. 
my sections two primary archesporial 
cells were usually present (Fig. 163 A, B), 
Fic. 162. somewhat as in Lycopodium inundatum. 
Selaginella Martensti, Spring. Sporangia Tangential sections show that these 
in radial section. A traverses the stem apex f h i 
(ap), the sporophyll (/), and sporangium (x); | Tepresent two rows of archesporial cells, 
aude Ssteeean eee X3s0, + With about four cells in each (Fig. 163 p). 
Thus the correspondence in sporangial 
type with that of Lycopodium is very striking, as regards early development: 
the chief difference is in the origin of the tapetum, for this in Selagine/la 
is cut off by tangential divisions from the sporogenous tissue (Fig. 163 c, E), 
of which it is thus a sterilised part. There is reason, however, to think 
that the first periclinal divisions in the young sporangium do not always 
1 Observations have been made on various species of the genus: Goebel (of. Zeit., 
1881, p. 697) investigated S. spznilosa, helvetica, and Wallichiz, and his results are 
restated in his Organography, vol. ii.; p. 600; allowance is, however, made by him for some 
degree of variation in details. My own observations on S. spzmulosa, and Martensii are 
described in my Stzdzes, i., p. 522. Campbell, in his Aosses and Ferns, 2nd edition, 
p- 530, describes the development for S. Avrazssiana, but his figures are by no means 
convincing that his reference of the whole sporogenous tissue to a single parent cell in 
the radial section is correct. Miss Lyon (Bot. Gaz., xxxii., p. 124) has made a 
careful study of the development in S. afus, and rzpestris, and traces the sporangium 
frequently if not always to a single superficial cell, which she designates the archesporium; 
but as the results from radial sections were not accurately checked by comparison of 
tangential or transverse sections, the point of ultimate origin of the whole sporangium 
from a single superficial parent cell cannot be regarded as demonstrated for this species. 
Before the details for the genus as a whole can be properly understood, the development 
will have to be studied in tangential as well as in radial sections, in a number of different 
species selected from different sections of the genus; meanwhile the substantial agreement 
of the sporangial type between the less differentiated S. spzmulosa and the genus 
Lycopodium is the main point of interest for the present discussion. 
