468 MICROSCOPICAL OBSERVATIONS 



and I accordingly examined nnraerous species of many of 

 the more important and remarkable families of the two great 

 primary divisions of Phsenogamous plants. 



In all these plants particles were found, which in the 

 different families or genera, varied in form from oblong to 

 spherical, having manifest motions similar to those already 

 described ; except that the change of form in the oval and 

 6] oblong particles was generally less obvious than in Ona- 

 grarise, and in the spherical particle was in no degree ob- 

 servable.^ In a great proportion of these plants I also 

 remarked the same reduction of the larger particles, and a 

 corresponding increase in the molecules after the bursting 

 of the antherse : the molecule, of apparently uniform size 

 and form, being then always present ; and in some cases, 

 indeed, no other particles were observed, either in this or 

 in any earlier stage of the secreting organ. 



In many plants belonging to several different families, but 

 especially to Graminese, the membrane of the grain of pollen 

 is so transparent that the motion of the larger particles 

 within the entire grain was distinctly visible ; and it was 

 manifest also at the more transparent angles, and in some 

 cases even in the body of the grain in Onagrarige. 



In Asdepiadea, strictly so called, the mass of pollen filling 

 each cell of the anthera is in no stage separable into distinct 

 grains ; but within, its tesselated or cellular membrane is 

 filled with spherical particles, commonly of two sizes. Both 

 these kinds of particles when immersed in water are gene- 

 rally seen in vivid motion ; but the apparent motions of the 

 larger particle might in these cases perhaps be caused by 

 the rapid oscillation of the more numerous molecules. The 

 mass of pollen in this tribe of plants never bursts, but merely 

 connects itself, by a determinate point, which is not unfre- 

 quently semitransparent, to a process of nearly similar con- 

 sistence, derived from the gland of the corresponding angle 

 of the stigma. 



1 In Lolium perenne, however, which I have more recently examined, though 

 the particle was oval and of smaller size than in Onagrarise, this change' of form 

 was at least as remarkable, consisting in an equal contraction in the middle of 

 each side, so as to divide it into two nearly orbicular portions. 



