SPERMATOPHYTES 
257 
which is the more or less elongated, stalklike region (figs. 572-574). 
It should be noted that such a term as anther is one of convenience 
rather than of morphological exactness, for it is made up of a complex 
of sporangia and sporophyll. 
Microsporangia. The sporangia develop as in gymnosperms, being 
of the eusporangiate type. A transverse section of a very young anther 
shows a mass of homogeneous tissue invested by the epidermis. The 
layer just beneath the epidermis (hypodermal layer) is potentially 
sporogenous; but usually it becomes actually sporogenous in four 
regions, which in transverse section show a variable number of cells 
(one to several). Of course 
these regions of initial cells 
are really four longitudinal, 
hypodermal bands of varying 
width. Each one of these 
bands of initials divides peri- 
clinally, forming two layers 
of cells (fig. 575). The outer 
layer (just beneath the epi- 
dermis) is the primary wall 
layer; the inner one is the 
primary sporogenous layer. 
The primary wall layer di- u FlGS ' 57*-574. - Stamens of angiosperms, 
... f . showing anther and filament : 572, ordinary type, 
Vldes further, forming several w ; t h longitudinal dehiscence; 573, Solanum, with 
(usually three to five) wall dehiscence by terminal slit or pore; 574, Vac- 
layers (fig. 576). The outer- cinium > with tubular P r lon g ations of P Uen sacs 
^ ' . for dehiscence. After KEENER. 
most wall layer is usually 
much modified, the cells becoming large and conspicuously banded, 
forming the so-called endothecium (fig. 580), a layer that assists in the 
dehiscence of the sporangium. The innermost wall layer usually 
becomes transformed into a portion of the tapetum, the nutritive layer 
of the sporogenous tissue (figs. 576, 577). The intermediate layers are 
the middle layers, and usually become more or less flattened and dis- 
organized through the activity of the tapetum. A section through a 
completed sporangium wall, therefore, reveals the epidermis, the 
endothecium, one or more middle layers, and the tapetum (fig. 577). 
The cells of the primary sporogenous layer usually divide two or three 
times (sometimes oftener, and sometimes not at all), forming the spore 
mother cells (fig. 577). In the two successive divisions of the mother 
