THE HIGHER CRYPTOGAMIA. 387 



slightly developed, are pushed so far upwards on the upper 

 surface of the next lower leaf that they appear to form a 

 portion of it (PL LIV, fig. 1 ; PI. LVI, fig. 30). In the 

 vascular cryptogams there are the like difficulties in obtain- 

 ing a clear idea of the relation of the sporangium to the 

 leaf, as are met with in observing the relations between the 

 placenta and ovules of phsenogams, and the carpels. The same 

 considerations must find a place here, and on this account 

 I would withdraw my former assent to the explanation * of 

 the sporangium of Selaginella given by Bischoff, who 

 described it as a metamorphosed axillary bud, and adopt 

 von Mold's view, the probability of the correctness of 

 which is supported by the relation between the sporangium 

 of Isoetes and its leaf and leaf-scale, the latter being the 

 manifest analogue of the stipules of Selaginella. 



As the sporangium becomes older the spore -mother- cells 

 become individualised, after a moderate thickening of their 

 walls. They then form spherical cells with turbid mucila- 

 ginous contents and a rather large nucleus. They are 

 closely crowded together and fill the cavity of the fruit 

 (PI. LV, fig. 6). 



Up to this point the history of the development of all 

 sporangia is the same. Henceforth however, as in all the 

 Rhizocarpese, the subsequent development exhibits essen- 

 tial differences, according as the sporangia are destined to 

 become microsporangia or macrosporangia, i. e. to produce 

 small or large spores. In Selaginella hortensis the lowest 

 sporangium only of each mass of fruit becomes a macro- 

 sporangium ; that one, namely, which is formed in the axil 

 of the lowest one of that longitudinal row of aristate 

 leaves which is situated vertically over the last primary leaf 

 on the right or left side of the shoot of the preceding 

 order. By the rapid and remarkable increase in size of the 

 fruit the latter grows beyond the lateral margins of its own 

 covering leaf, so that the two next lower ones also, which 

 are sterile leaves belonging to other longitudinal rows of 

 the fruit-ear, have to take part in covering the fruit. 



Of the many free spherical cells of the interior of the 

 young macrosporangium, one single cell only, not distin- 



* Vergl. Unters.,' p. 119. 



