43i 
Morphology of Cycadean Sporangia. 
The two layers of cells, the origin of which from the cells 
of the wall adjoining the sporogenous mass was described 
above, are now so crushed that the limits of the cells are 
difficult to make out, and the whole appears under low 
powers as a thin band outside the tapetum (Fig. 15). The 
cells of this layer stain deeply, and are sharply distinguished 
from the outer cells of the wall, which have oval nuclei of 
granular appearance. There are three to six layers of these 
cells and the wall is bounded by the epidermis, the cells 
of which differ in form and structure according to the part 
they play in the dehiscence of the sporangium. 
When examined from the surface, the epidermal layer is 
seen to consist of cells with more or less thickened walls, 
elongated in the direction parallel to the line of dehiscence. 
The latter is distinguished by its colourless cell-walls, which 
contrast with the brown colour of the cells of the rest of the 
wall. Its cells, which form two rows, are somewhat shorter 
than those on either side ; they have greatly thickened walls 
in which numerous simple pits are present. The line of 
dehiscence extends along the whole length of the side of the 
sporangium which is turned away from the sporophyll ; it 
reaches from close to the stalk almost to the apex, where it is 
continuous with a group of cells which agree with it in the 
appearance and structure of their walls, but have more or less 
circular cavities. These cells which occupy the apex, corre- 
spond in position, as Warming has stated 1 , to what is usually 
described as the annulus of Osmnnda or Angiopteris. In 
Stangeria they do not project above the level of the surround- 
ing cells, though this is the case in some other genera of 
Cycadaceae 2 . The apex of the sporangium of Stangeria 
corresponds closely with that of Ceratozamia. The cells 
of the rest of the sporangial wall have cell-walls of a yellow 
colour and of considerable thickness. When viewed from the 
outside but little difference can be detected between them : 
the cells near to the line of dehiscence have, however, some- 
1 Warming, loc. cit. p. i, PI. V, Fig. 12. 
2 Treub , loc. cit. p. 3 7, PI. Ill, Fig. 2. 
