38 



NATURAL HISTORY OF PLANTS. 



gynseceum is unicarpellary, with a sessile or stipitate one- celled 

 ovary, surmounted by a terminal style whose stigmatiferous apex 



Acacia arabica (Own-Arabic Plant). 



Fio. 28. 

 Habit (f). 



may or may not be dilated and convex or concave. 1 Within the 



cnliar structure, presenting what H. Mohl has 

 termed {Ann. Sc. Nat., ser. 2, iii. 229, t. 10, 11, 

 figs. 42, 43,) " the form of the Mimosea." He 

 writes : " Each separate pollen grain (and there 

 are but eight to each anther) consists of sixteen 

 cells closely bound 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. Rosanoff 

 (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. Bentiiam (Gen., 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. 



