CHAP. II. 
POLLEN. 
151 
received particular illustration from Purkinje, who calls it 
endothecium^ and who has found that it consists of that very 
remarkable kind of tissue which has been already described 
under the name of fibro-cellular. According to that bo- 
tanist the forms of this tissue are extremely variable, the 
bladders being sometimes oblong, sometimes round, frequently 
cylindrical, usually fully developed, or, in some cases, merely 
rudimentary; the bladders are in some species erect, in others 
decumbent ; but in all cases more or less fibrous. (See Plate I. 
figs. 4. 13, 14, 15. 18, 19, 20.) For an elaborate treatise on 
the subject see Joh. Ev. Purkinje de Cellulis Antherarum 
Fibrosis, Vratislaviae, 1830. 4to, with 18 plates. 
The pollen is the pulverulent substance which fills the cells 
of the anthers : it consists of a multitude of little grains, 
most commonly called granules^ or sometimes utriculi, 
Gleichen considered pollen to take its origin in the midst 
of a mucilaginous mass, occupying the cells of the anther, and 
merely becoming indurated and solidified towards maturity. 
Brown, in the year 1820, without entering into any details on 
the subject, described it [Linn. Trans, xiii. 211.) as produced 
on the surface or in the cells of a pulpy substance with which 
the thecae are filled. But this hypothesis is objected to by 
Link (Elem, 294.). Guillemin (Recherches p. 5.) declares that 
the granules are always arranged in regular rows, and gene- 
rally in the direction of the valves, and that they are always 
distinct, at first floating in a viscid liquid, but finally quite 
separate from it. Adolphe Brongniart concludes, from a 
series of very interesting observations, " that the pollen is 
formed in the interior of the cells of a single and distinct 
cellular mass, which fills each cavity of the anther without ad- 
hering to its walls, and consequently without being a continu- 
ation of the parenchyma of that organ, from which it also 
differs in the size and form of the cells that compose it ; that 
sometimes these cells, which are at first in close cohesion, se- 
parate from each other, when each becomes a grain of pollen ; 
and that sometimes the cells contain an uncertain number of 
g rains of pollen, which, at the time of their perfect de velopemen t, 
rupture and almost entirely destroy their membrane, some 
L 4 
