312 Remarks on the Impregnation of Plants. 
tensible membrane. ‘The cavity is filled with a fluid, which, under 
a powerful lens, appears slightly turbid, on account of a vast number 
of minute granules which float in it. The existence of an inner 
lining to the pollen-grains was ascertained at an early period, first by 
Needham and afterwards by Koelreuter, and, although since doubt- 
ed, the correctness of their observations has lately been abundantly 
confirmed by the admirable researches of Ad. Brongniart and Mir- 
bel. An account of some recent observations by the last named — 
author is appended to his incomparable memoir on Marchantia, 
where he has also given a representation of the two coats. 
A magnifying power of two or three hundred diameters reveals 
the existence of two kinds of granules in the fluid of the pollen-. 
grain. The larger kind, which are also the fewer in number, have 
been particularly examined by Ad. Brongniart and Brown, whose 
researches, made about the same time and wholly independently of 
each other, coincide in almost every particular.* These granules 
are peculiar to pollen, and have been detected in every plant that 
been submitted to examination. They differ in shape in differ- 
ent plants, but are uniform in the same species. The following is 
extracted from the account of these granules given by R. Brown, 
as they appeared in the pollen of the plant which he first submitted 
to examination. ‘This plant was Clarkia pulchella, in which the 
pollen-grains, taken from the anthers when completely developed 
but before their dehiscence, were filled with particles or granules of 
a size varying from the 4000th to about the 5000th of an inch in 
length, their form being intermediate between cylindrical and oblong, 
slightly flattened perhaps, the extremities being rounded and equal. 
While examining the form of these particles floating ina drop of wa- 
ter, IL observed that many of them were evidently in motion. Their 
movements were not confined to a mere change of place in the fluid, 
as manifested by modifications in their relative position, but there 
was frequently a change of form in the particle itself; and several 
times a contraction or incurvation was perceived near the middle of 
a particle on one side, accompanied by a corresponding convexity 
on the opposite side. In some instances the particle was seen to 
wisp ie Lataneno—FannipitanaMe 
* These granules were discovered and described by Needham as long ago as 
the year 1750. He even suggests that they penetrate to the ovule and form the em- 
0. ‘This isnot the only instance in which the observations and suggestions of 
this author, after having been doubted or left in obscurity for nearly seventy 
years, have been. recently confirmed, or rendered extremely probable. 
