PLANT ORGANS AND ORGANISMS 1 91 



rarely the anthers may be two-celled in their young state and by the 

 breaking down of the partition become one-celled, e.g., Malvacea, 



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 endothecium. The outer- 

 most one to three layers of this become spirally, annularly or stel- 

 lately thickened to form the elastic tissue of the anther, which, by 

 pressure against the delicate epidermis or exothecium, causes ulti- 

 mate 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 pollen or microspore cells. Filling the 

 cavities of the four sporangia are the mature pollen grains. The 

 connective shows in or near its center a vascular bundle with xylem 

 uppermost and phloem downward, surrounded by thin-walled cellu- 

 lar tissue, from which the indusial and sporangial substance has 

 matured by extension. 



Anther Dehiscence. This is the breaking open of the anther to 

 discharge the pollen. 



When fully ripe the dividing partition between each pair of spor- 

 angia usually becomes thinned, flattened and ultimately breaks down, 

 while the elastic and resistant endothecium, steadily pushing against 

 the more delicate and now shrinking exothecium causes rupture 

 where endothecium is absent, namely along opposite lines of the 

 anther wall. Thus arises a line of anther dehiscence called longi- 

 tudinal anther dehiscence on either side of the anther sacs. In the 

 .division Solanece of the family Solanacecz which includes Belladonna, 

 in some of the Ericacece as Rhododendron and Azalea, etc., the 

 anthers dehisce by small apical pores from which the pollen is shed. 

 This kind of dehiscence is called apical porous dehiscence. Again, 

 in Lauracece and Berberidacecz, the anthers dehisce by recurved valves. 

 This is called valvular dehiscence. 



Moreover, in Malvacea the originally longitudinal anther is divided 

 internally by a partition. It gradually swings on the filament so 

 that eventually the anther is transverse and the partition becomes 



