38 
NATURAL HISTORY OF PLANTS. 
gyneceum is unicarpellary, with a sessile or stipitate one-celled 
ovary, surmounted by a terminal style whose stigmatiferous apex 
Acacia arabica (Gum-Arabie Plant). 
Fie. 28. 
Habit (3). 
may or may not be dilated and 
Within the 
convex or concave.’ 
culiar structure, presenting what H. Mout has 
termed (Ann, Se. Nat., sér. 2, iii. 229, t. 10,11, 
figs. 42, 43,) “the form of the Mimosee.” He 
writes: “ Each separate pollen grain (and there 
are but eight to each anther) consists of sixteen 
cells closely hound together, and arranged so that 
there are two layers of four cells each in the 
centre, with a rim of eight cells around them, so 
that the whole grain is lenticular.” Other grains, 
he says, consist of eight cells, the four above 
alternating with the four below. S. RosaNnorF 
(Jahrb. f. Wiss. Bot., iv. 441) has observed that 
in an empty anther-cell of an Acacia there are 
four excavations separated by crucial septa. 
‘The four cells which corresponded with these were 
four mother-cells of the compound pollen-grain. 
These cells, says he, divide by centripetal septa 
springing from the wall of the mother-cell. 
Later on the layers interposed between the 
mother-cells undergo partial absorption and 
granular degeneration. BrEntHaM (Gien., 464) 
describes the pollen grains as aggregated in each 
cell, from two to six in number. In the species 
belonging to the section Albizzia, MoHL seems 
to have found the number of eight in each 
anther quite constant. 
1 The summit of the style is usually bent on 
itself in a variable way in the bud, as are the 
staminal filaments by which it is surrounded, 
