POLLEN. 



[ 516 ] 



POLLEN. 



granular and spiny, to pseudo-cellular arising 

 from reticulated ridges ; in addition to this, 

 the processes just alluded to give a very 

 peculiar aspect to many kinds of pollen. 

 Besides these, we find in all cases markings 

 appearing like pores, or others hke slits 

 (which become furrows when dry), or both 

 together, and these in varying number in 

 different cases. The colour of the pollen 

 presents great differences ; although usually 

 yellow, it may be whitish, red (Verbascum), 

 blue {Epilobiiim angustifolium), even black 

 (tulip) ; this colour resides in the outer 

 coat. The outer coat also exhibits, in the 

 majority of cases, a secretion upon its sur- 

 face, of a viscid character, usually described 

 as oily, but apparently consisting of a viscid 

 matter, not readily soluble in water, remain- 

 ing from the dissolved parent-cells. It 

 would seem to be this substance which holds 

 together the pollen-grains in those cases 

 where it consists of waxy masses, readily 

 breaking up into small fragments ( Ophry deous 

 Orchids). In the Onagracese the pollen-grains 

 are loosely connected by slender, viscid fila- 

 ments, which appear to be derived from the 

 same source. 



The more detailed explanation of the 

 characters of the pores, &c., the projecting 

 processes, and the compound conditions of 

 pollen, will be understood better after a 

 sketch of its development. 



The anther, in which the pollen is formed, 

 consists in its younger stages of a minute, 

 solid, cellular papilla or cylindrical body; at 

 an early period a distinction becomes mani- 

 fest in its cells ; a single vertical row, lying 

 in the position of the axis of each pollen- 

 chamber (or loculus), presents a different 

 aspect, from its cells exceeding the surround- 

 ing ones in size ; and these rows undergo 

 a special development to produce the pollen- 

 grains, while the surrounding layers are 

 developed into the tissues forming the coat or 

 wall of the anther, and its midiib or con- 

 nective (see Anther). The cells of the pri- 

 mary row multiply by cell-division, with 

 the general increase in size of the anther 

 (figs. 597-599), until at length they form 

 relatively large masses of cellular tissue, 

 composed of large squarish cells, filled with 

 granular contents, well defined as constitu- 

 ting a distinct tissue from the walls of the 

 pollen-chambers. A new change then takes 

 place; the contents of each cell secrete a 

 layer of cellulose, which does not adhere to 

 the wall of the parent-cell to form a layer of 

 secondary deposit, but lies free against it, so 



that a new free cell is formed within each 

 old one, nearly filling it. The walls of the 



Fig. 597. 



Fig. 598. 



C I C M 



Fig. 599. 

 CL CI CM GE 



Vertical section of a cell of a young anther of the 

 melon, showing the gradual separation of the regions. 

 C E, epidermal cells ; CI, cells of the wall of the anther; 

 C L, cells lining the loculi ; C 31, cells from which the 

 poUen is developed. 



Magnified 100 diameters. 



old cell (forming a connected parenchjonatous 

 tissue) then dissolve, so that the free cells 

 become free, no longer merely in their parent- 

 cells^ but in a cavity which is to constitute 

 the pollen-chamber or loculus of the anther. 

 These free cells are the parent-cells of the 

 pollen of authors. A new phenomenon soon 

 occurs in these. These parent-cells divide 

 into four by ordinary cell-division, either by 

 one or by two successive partings by septa 

 at right angles to each other, but both per- 

 pendicular to an imaginary axis (as when an 

 orange is quartered), or by simultaneously- 

 formed septa, which cut off portions in such 

 a manner that the new cells stand in the 

 position of four cannon-balls piled into a 

 pyramid (tetrahedrally). These new cells 

 are the special parent-cells of the pollen, 

 and in each of these the entire protoplasmic 



