252 



ORGANOGRAPHY. 



assisted in promoting the dehiscence of the anther. "We have 

 now more particularly to describe the mode of development and 

 structure of the pollen. 



The formation of the pollen may be described as follows : — 

 The large cells {fig. 498, cm), which are developed in the paren- 

 chyma of the young anther, and which are destined for the for- 

 mation of the"^ pollen, are called 'parent or mother cells : the 

 primordial utricle of each of these becomes infolded, so as to 

 divide it into four portions, either directly, or indirectly by first 

 dividing it into two, and then each of these being again divided 

 into two others {fig. 546, a, b, c, d); these four portions are called 

 special pareoit or mother cells ; the whole of the protoplasniic 

 contents in each cell then secretes a layer of membrane on its 

 outside, and we have thus four perfect cells {fig. 546, d), which 

 constitute t\ie. irwQ pollen-cells, formed in the cavity of the parent 

 cell. As these pollen-cells progress in development, and increase 



Fiq. 546. 

 b 



Fig. 547. Fig. 548. 



Fig. 546. Formation of the rollen in the Hollyhock (Althcpa rosea). After 

 Mohl and Henfrey. a. shows four nuclei in the parent cell, and four 

 septa commencing to be formed. The primordial utricle and cell-con- 

 tents are contracted by the action of alcohol, b. The development of 

 the septa more advanced, c. The primordial utricle removed from the 

 jiarent cell, but not yet completely divided into four parts, d. The 

 division of the parent cell into four parts completed, and each part 



containine: one pollen-cell. Fig. 547. Pollen of Inga unoinala. 



Fig. 548. Pollen of Periploca grceca. After Jussieu. 



in size, they distend the parent cell and ultimately cause its ab- 

 sorption ; and subsequently, by their continued growth, the 

 special mother cells are generally absorbed also, by which the 

 pollen-cells are set free in the loculus of the anther in their 

 perfect condition. Sometimes the membrane of tlie special 

 parent cells is not completely absorbed, in which case the pollen- 

 cells of the parent cell are more or less connected, and form a 

 compound body consisting of four pollen-cells, as in Feriploca 

 gr(sca {fig. 548) ; or if the membranes of two or more united 

 parent cells are also incompletely absorbed, we may have a mass 



