360 COLOUR OF POLLEN FOVILLA. [BOOK i. 



slits many kinds of pollen have circular holes, varying in 

 number, in different species, from one to an indefinite quan- 

 tity in the Hollyhock (Alcea rosea). Under these holes 

 Fritzsche finds small, plano-convex, lenticular, intermediate 

 bodies (zwischenkorpern) , lying between the extine and the 

 iiitine, with their convexity reposing upon the latter; he 

 represents them as particularly large in some Mallowworts. 



The colour of pollen is chiefly yellow. In Epilobium angusti- 

 foliurn and many Polemoniads it is blue ; in Verbascum it is 

 red ; and it occasionally assumes almost every other colour, 

 except green. 



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 sub- 

 ject, 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 distinguishable from the moving, ultimate, organic mole- 

 cules common to all parts of a vegetable ; the other, much 

 larger, often oblong, and unlike any other kind of particle 

 hitherto detected in plants. Clarkia pulchella, and some other 

 Onagrads plants, show this difference, as well as the motion, 



