PLANT ORGANS AND ORGANISMS 
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a dilated base as in the Harebell, three-toothed as in Garlic, appen- 
diculate, when it bears an appendage as in Chcetostoma, Alyssum, etc. 
The filament is covered with a protective epidermis containing 
stomata. Beneath this is a soft, loose cellular tissue, the mesophyll, 
and in the center a small vascular bundle, the pathway of food from 
the floral axis to the anther. In some cases the single bundle may 
split into two or three bundle parts. 
Gross Structure and Histology of the Anther. — Each staminal leaf 
(microsporophyll) bears a special development or appendage as a 
rule on its extremity which is the anther or microsorus. This consists, 
fundamentally, of a median prolongation of the filament equal to the 
connective or placenta. This develops on either side a quantity of 
indusial tissue that grows out to form a covering substance that 
protects and carries two microsporangia on either side. An anther 
therefore consists of a median connective or placenta, producing on 
either side two anther lobes or indusial expansions. Each anther lobe 
encloses two pollen sacs or microsporangia which, in some cases, 
remain distinct up to the dehiscence (splitting open) of the anther. 
Thus in Butomus , the anthers show four pollen chambers up to the 
time of dehiscence. Again in various species of Lauracece, the 
anthers remain four lobed and dehisce by four recurved lids. But in 
the great majority of Angiosperms each pair of pollen sacs fuse before 
dehiscence, owing to the breaking down of the partition between 
them, and so, at that time, show two-celled anthers. Still more 
rarely the anthers may be two-celled in their young state and by the 
breaking down of the partition become one-celled, e.g., Malvaceae. 
Externally the mature anther is bounded by an exothecium or epi- 
dermis, often swollen, where lines of dehiscence occur, which may 
develop stomata, also hairs. Within it is a combined layer or set of 
one to often two or three, sometimes five or six cell layers (Agave, etc.) 
of indusial and sporangial cells, the endothecmm. The outermost one 
to three layers of this become spirally, annularly or stellately thickened 
to form the elastic tissue of the anther, which, by pressure against the 
delicate epidermis or exothecium, causes ultimate rupture of the 
anther wall. Within the innermost endothecial layer, bounding each 
sporangium, is the tapetum, a single-celled layer. This, near the time 
of dehiscence, undergoes breaking down or absorption by developing 
