388 
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 Lycopodiimi, that they come to stand in the axils of the 
leaves : in Selagmella they arise from the stem, and in Psilotum and Tmesipteris 
from lateral branches. In the earliest stage of their development they are in the 
Filicineae 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 Rhizocarpeae and Selaginelleae 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. 1880-81. 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 ; Rhizocarpeae. 
Eusporangiata. The sporangium is developed from several cells, w^hich, except in the case of 
Iso'eles, are all superficial. 
a. Archesporium unicellular ; tapetum derived not from it, but from the tissue of the sporangium. 
Ophioglosseae ; Marattiaceae ; Equisetaceae. 
b. Archesporium unicellular; tapetum derived from it. 
Psilotmn ; Tmesipleris {7). 
c. Archesporium unicellular ; tapetum derived partly from it, and partly from the tissue of the 
sporangium. 
Selagmella. 
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.'\ 
