THE FLOWER 279 
by developing PoLLEN or microspore cells. Filling the cavities 
of the four sporangia are the mature pollen grains. ‘The con- 
nective shows in or near its center a vascular bundle with xylem 
uppermost and phloem downward, surrounded by thin-walled 
cellular tissue, from which the indusial and sporangial substance 
has matured by extension. 
ANTHER DeEHISCENCE.—This is the breaking open of the 
anther to discharge the pollen. 
When fully ripe the dividing partition between each pair of 
sporangia 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 /ongitudinal anther dehiscence on either side of the 
anther sacs. In the division Solanee of the family Solanacee which 
includes Belladonna, in some of the Evicacee 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 Lauracee and Berberidace@, the anthers 
dehisce by recurved valves (see Fig. 202). 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 par- 
tition becomes absorbed, thus becoming a one-celled anther 
with transverse dehiscence in its mature state [see Fig. 194 (11)]. 
DEVELOPMENT OF THE ANTHER.—Each stamen originates as a 
knob-like swelling from the receptacle between the petals and 
carpels. This swelling represents mainly future soral (anther) 
tissue. The filament develops later. When such a young sorus 
or anther is cut across and examined microscopically, it shows a 
mass of nearly similar cellular tissue in which the first observable 
changes are the following: 
The surface dermatogen cells become somewhat flattened and 
regular to form the future epidermis or exothecium of the anther. 
About the same time, some cells, by more rapid division in the 
middle of the anther substance, give rise to the elements of the 
