c^ScS VASCULAR CRYPTOGAMS. 



axillary branching, in the sense in which the term is applied to Phanerogams, 

 probably does not occur here. 



The Development of the Sporangia^ is in most cases evidently a function of 

 ordinary or of specially modified leaves ; it is only when they arise singly upon the 

 upper surface of leaves, as in Lycopodium, that they come to stand in the axils of the 

 leaves: in Selaginella they arise from the stem, and in Psilotum and Tmesipteris 

 from lateral branches. In the earliest stage of their development they are in the 

 Filicinese outgrowths of single epidermic cells : in the other Vascular Cryptogams 

 they are developed from a group of cells. [The mother-cells of the spores are 

 derived from one or more cells which lie at first immediately beneath the epidermis 

 of the sporangium (hypodermal), and which Goebel terms the archesporium. The 

 archesporium becomes invested by one or more layers of cells, derived either from 

 the division of its own cells or of the cells forming part of the sporangium, to which 

 the name of tapetum is given. As the sporangium ripens, the cells of the tapetum 

 usually become absorbed, and the mother-cells of the spores become isolated from 

 their combination into a tissue. From each mother-cell four spores are developed : 

 this takes place in two ways ; either the cell is divided into two by a cell-wall after 

 the nucleus has divided, and this process is repeated in each of the two daughter- 

 cells, or the nucleus divides into two and each of these again into two before any 

 cell-wall is formed. The latter is by far the more general mode. The distinction 

 between macrospores and microspores in the Rhizocarpese and Selaginellese is 

 manifested only after the division into four of the mother-cells which were pre- 

 viously alike.] 



It is clear from what has now been said that the sporangium of Vascular 

 Cryptogams is equivalent, from a physiological but not from a morphological point 

 of view, to the sporogonium of Mosses. This latter forms by itself the whole of 

 the asexual generation of Mosses ; while the sporangium of Vascular Cryptogams 



^ [On the Comparative Development of the Sporangia see Goebel, Bot. Zeitg. 1 880-81. He 

 classifies the Vascular Cryptogams according to the mode of development of their sporangia, as 

 follov/s : — 



Leptosporangiata. The sporangium is developed from a single epidermal cell. The arche- 

 sporium is a single cell, and the tapetum is derived from it. 

 Filices ; Rhizocarpese. 



Eusporangiata. The sporangium is developed from several cells, which, except in the case of 

 Tsoeies, are all superficial. 



a. Archesporium unicellular ; tapetum derived not from it, but from the tissue of the sporangium. 

 Ophioglossese ; Marattiacese ; Equisetacese. 



b. Archesporium unicellular ; tapetum derived from it. 

 Psilotum; Tmesipteris {?). 



c. Archesporium unicellular ; tapetum derived partly from it, and partly from the tissue of the 

 sporangium. 



Selaginella. 



d. Archesporium multicellular (a row^ of cells) ; tapetum formed not from it but from the tissue 

 of the sporangium. 



Lycopodium. 



e. Archesporium multicellular (a layer of cells) ; tapetum derived from it. 



Isoetes. 

 The Phanerogams also belong to the Eusporangiata, see infra.] 



