FUNDAMENTAL OEGANS. 



133 



let us examine their structure in the adult, and their mode of development in the 

 young stamen. 



The filament consists of a central bundle of trachese which traverses its length, 

 of a layer of cells enveloping this bundle, and of a thin superficial epidermis. The 

 connective, which is the continuation of the filament, is formed of cells of the con- 

 sistence of glandular tissue, in which the bundle of tracheae terminates. 



The anther is usually divided into two cavities, separated by the connective, and 

 containing the pollen. The walls of these cells consist of an outer 

 or epidermal layer of cells (fig. 699, CE) with many stomata, and of 

 an inner simple or multiple layer of fibrous (E), annular, spiral, or CE 

 reticulated cells ; this layer becomes thinner as it approaches the line 

 of dehiscence of the anther, where it ends. At the period of dehis- Bemamsof the'nbrous 

 cence the outer membrane of these cells is destroyed, and the little dermis of the anther 

 netted, ringed, or spiral bands which lined it alone enclose the pollen, 

 the emission of which they assist when they dry up, contract, and separate the valves 

 of the anther. The young stamen appears as a cellular green papilla, which usually turns 

 yellow. The anther is the first formed ; it presents a median furrow (the connective) , 

 and two lateral ones (the future lines of dehiscence) ; the filament appears next, at first 

 wholly cellular, then traversed by a bundle of tracheae. The tissue of the anther is at 

 first a uniform cellular mass (fig. 700), in the middle of which a certain number of 

 cells are absorbed and leave usually four spaces, which gradually enlarge and form as 

 many cavities, nearly equidistant from the centre and the periphery. Each pair of 

 these small cavities eventually represents an entire cell (fig. 701). All these four 



CL Cl CM CE 



C.I c.E CE C.i CM 



700. Melon. 



Vertical section of young 

 anther (mag.), showing 

 the epidermal cells (CE), 

 and the inner cells (ci), 

 all alike and homoge- 

 neous, in the middle of 

 which spaces will form. 



701. Melon. 



Vertical section of an anther- 

 cell (mag.) with two cellules. 

 CE, epidermal cells; c I, inner 

 cells ; c M, mother-cells con- 

 tained in the cellules. 



702. Melon. 



Vertical section of an anther-cell 

 where the cellules are filled with 

 mother-cells, c L, walls of the 

 cellules (mag.). 



CM-/ 



P. 



703. Melon. 

 Mother cells (c M), 

 originally hexagonal, 

 of which the septa are 

 destroyed, and con- 

 taining each four 

 pollen - grains (p) 

 (mag.). 



cavities gradually fill with mucilage, out of which are elaborated two forms of 

 cellular tissue, one of small cells (fig. 702, CL) that line the cavity, the other of large 

 cells (CM) that fill the cavity, and within which the pollen is developed. The latter, 

 called mother-cells (CM), soon become filled with a fluid full of granules; the granules 

 again aggregate, and form four nuclei floating in the liquid, which thickens by 

 degrees from without inwards, and finally forms four septa dividing the mother-cells 

 into as many cellules. Each, nucleus then becomes coated with a membrane (fig. 



