190 
ORGANOGRAPHY. 
BOOK I. 
definite quantity in Alcea rosea. Under these holes Fritzsche 
finds small, plano-convex, lenticular bodies (zimschenkdrpem)^ 
lying between the extine and the intine, with their convexity 
reposing upon the latter ; he represents them as particularly 
visible and large in some Malvaceae. 
The colour of pollen is chiefly yellow. In Epilobium an- 
gustifolium and many Polemoniaceae it is blue; in'Verbascum 
it is red; and it occasionally assumes almost every other colour, 
except green. According to Fourcroy and Vauquelin, the 
pollen of the Date tree consists of malic acid, phosphate of 
magnesia and lime, and also of an insoluble animal matter 
intermediate between gluten and albumen. Macaire Prinsep 
has ascertained that the pollen of the Cedar contains malate 
of potass, sulphate of potass, phosphate of lime, silica, sugar, 
gum, yellow resin, and a substance which, by its characters, 
approximated to starch. Being analysed as a whole, it gave, 
per cent., 40 carbon, 11*7 hydrogen, and 48*3 oxygen, but 
no nitrogen. — Bihl. Univers. 1830. 45. 
The matter contained in the granules is called the fovilla. 
Under common magnifiers it appears like a turbid fluid; 
under glasses of greater power it has been found to consist of 
a multitude of particles moving on their axes with activity, of 
such excessive minuteness as to be invisible unless viewed 
with a magnifying power equal to 300 diameters, and mea- 
suring from the 4000th or 5000th to the 20,000th or 30,000th 
of an inch in length. This motion was first distinctly noticed 
by Gleichen ; but it seems to have escaped the recollection of 
succeeding botanists until the fact was confirmed by Amici, 
who some time before 1824 saw and described a distinct, 
active, molecular motion in the pollen of Portulaca oleracea. 
In 1825 the existence of this motion was confirmed by Guille- 
min, who ascertained its presence in other species. In June 
1827, I was shown the motion by Dr. Brown, who subse- 
quently published some valuable observations upon the subject, 
without, however, noticing those of either Amici or Guillemin. 
The most important addition that was made by Brown to the 
knowledge that previously existed, consisted in the discovery 
of the presence of two kinds of active particles in pollen ; 
of which, one is spheroidal, extremely minute, and not dis- 
