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 vai'iable, 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 aubject see Joh. Ev. Purkinje de Cellulis Antherarum 

 Fibrosis. Vratislaviae, 1830. 4to, with 18 plates. 



The pollen is the pidverulent substance which fills the cells 

 of the anthers : it consists of a multitude of little srrains, 

 most commonly called (/ranules, or sometimes utricidi. 



Gleichen considered pollen to take its origin in the midst 

 of a mucilaguious 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 sm-face 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 w^alls, and consequently without being a continu- 

 ation of the parenchym_a 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 

 grains of pollen, w^hich, at the time of their perfect developement, 

 rupture and almost entirely destroy dieir membrane, some 



L 4 



