481 
formation of the tapetum, the remaming cells being spore-mother-cells. The tapetal 
cells then divide by transverse and longitudinal wails, so that the spore-mother-cells 
come to lie deeply within the tissue of the sporangium. 
In the macrosporangium of h'öetes each spore-mother-cell divides to form four 
macrospores ; its nucleus divides into two and each of these again into two, before 
any intervening cell-wall is formed. There is this peculiarity about the mode of the 
division, that the protoplasm, as in the delevopment of the spores of Anihoceros^ 
begins to divide before the nucleus. The spore-mother-cells of the microsporangium 
divide in a different manner, the only other known instance of the kind occurring in 
the pollen-mother-cells of Monocotyledons \ In them the nucleus divides into two, 
and this is followed by the formation of a cellulose wall between the two cells : the 
nucleus of each of these then divides, and a wall is formed between the resulting 
cells. It is in this way that the four ' special ' mother-cells of the microspores 
are produced.] 
Fig. 339.— a transverse section of the stem of Sela^nneila denticiilaia, the central vessels of the bundle not yet lignified; 
b air-cavity surrounding a bundle which is being given off to a leaf. 
Histology'^. Ill the Selaginelleae, to which group the following remarks more 
especially apply, the epidermis of the stem consists of long prosenchymatous cells 
between which no stomata occur. The cells of the epidermis have often beautifully 
sinuous lateral walls, and, like those of the Ferns, they contain chlorophyll which 
occurs in these cells as well as in the cells of the fundamental tissue of the leaf in the 
form of large granules, only a few of which are to be found in each cell (Fig. 44). The 
leaves usually possess stomata on the under surface only, but they occur on both surfaces 
of the small leaves of S. pubescens. In several species (such as S. stenophylla and Martensii) 
single epidermic cells occur with walls so thickened that the lumen is almost occluded. 
(Russow). In most of the species the epidermis of the upper differs from that of the 
under surface, in others {S, Galeotti, Kraussiana) the epidermis of the two surfaces is 
of the same nature. 
The Fundamental Tissue of the stem consists, as in Lycopodium, of elongated cells 
with septa which are either oblique or transverse : these cells retain, however, their 
thin walls and large cavities, in contrast to what is usually the case in the Lycopodieae, 
the hypodermal layers only becoming thick-walled (Fig. 340). It appears that the cells 
of the fundamental tissue, and consequently those of the other tissues also, are capable 
' [Strasburger, Zellbildung und Zelltheilung, 3rd ed., 1880, p. 167.] 
^ [For further details see De Bary, Vergleichende Anatomie, 1877. J 
I i 
