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 

 has 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 in a drop of wa- 

 ter, I 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 



* 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- 

 bryo. This is not 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. 



