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. 1 It has been seen above that S. spinulosa 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 6". spinulosa, 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), 

 somewhat as in Lycopodium inundatum. 

 Tangential sections show that these 

 represent two rows of archesporial cells, 

 with about four cells in each (Fig. 163 D). 

 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 Selaginella 

 is cut oft' 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 (Bot. Zeit., 

 1881, p. 697) investigated S. spinulosa, helvetica, and Wallichii, 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. spinulosa, and Martensii are 

 described in my Studies, i., p. 522. Campbell, in his Mosses and Ferns, 2nd edition, 

 p. 530, describes the development for S. Kratissiana, 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. apus, and rupestris, 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. spinulosa and the genus 

 Lycopodium is the main point of interest for the present discussion. 



FIG. 162. 



Selaginella Martensii, Spring. Sporangia 

 in radial section. A traverses the stem apex 

 (/), the sporophyll (/), and sporangium (x) ; 

 in the latter two archesporial cells are seen, 

 shaded. B shows an older stage. X 350. 



