PLANT ORGANS AND ORGANISMS 
Moreover, in Malvacece 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 
absorbed, thus becoming a one-celled anther with transverse dehis- 
cence in its mature state. 
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 fila- 
ment develops later. When such a young sorus or anther is cut 
across and examined microscopically, it shows a mass of nearly simi- 
lar cellular tissue in which the first observable changes are the 
following: 
The surface dermatogen cells become somewhat flattened and regu- 
lar 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 vascular 
bundle in the connective. Then, along four longitudinal tracts, rows 
of cells remain undivided or only divide slowly as they increase in size 
and around them cells divide and redivide to form the future endo- 
thecial and covering tissue to the four sporangia. Next, the four 
sporangial tracts of undivided cells cut off from their outer surfaces 
a layer of enveloping cells, the tapetum. This consists of richly proto- 
plasmic cells that form a covering to the spore mother-cells within. 
Each spore mother-cell undergoes division and redivision into four 
spore daughter-cells at the same time that reduction in the chroma- 
tin substance takes place in these cells. Thus originate tetrads 
(groups of four) of spore daughter-cells inside spore mother-cell wall. 
These continue to enlarge, press against the mother-cell wall which 
becomes converted into mucilage and each of the tetrad cells becomes 
in time a mature microspore or pollen grain. 
During this time the entire anther is growing in size, the cells of 
the endothecium in one or more layers becomes thickened by lignin 
deposits to form a mechanical endothecium; the tapetum gradually 
breaks down and appears only at length as an irregular layer around 
the maturing pollen cells. When the anther is finally ripe the parti- 
tion between each pair of microsporangia becomes narrowed, flat- 
tened and ruptured and thus numerous microspores or pollen grains 
