116 
POPULAR SCIENCE REVIEW. 
The pretty genus Polygala is characterised by a very remark- 
able form of pollen-grain. They are somewhat barrel-shaped, 
bulging in the middle, and with a considerable number (in P.myr- 
tifolia , fig. 21, from twenty to twenty-four) of regular longitudi- 
nal alternate ridges and furrows. They are very beautiful objects 
under the microscope. In the various species of Primula cha- 
racterised by “ dimorphic” flowers, the grains are small, shortly 
cylindrical rather than ellipsoidal, and with a varying number of 
furrows. There is also this remarkable peculiarity, that as far 
as my observation goes, the pollen-grains of the long-styled form 
are invariably smaller than those of the short-styled form ; at 
least this is the case in the primrose, cowslip, and polyanthus.* 
In figs. 22 and 23 we have the long and short-styled forms of 
the primrose, figs. 24 and 25 of the cowslip, and figs. 26 and 27 
of the polyanthus (transverse view). The explanation of this 
difference which has been suggested by Darwin and Lubbock, is 
a very ingenious and probable one. The long-styled form of 
Primula would of course require longer pollen-tubes to pene- 
trate the style in order to reach the ovules than the short-styled 
form. It is fertilised normally by the short-styled form, and 
this latter form is therefore provided with pollen-grains of 
a larger size. In Primula japonica (in which I am not aware 
whether the two forms occur) the form of the pollen-grain is 
very different (fig. 28) — a triangular plate with three deep fur- 
rows. Occasionally in anemophilous flowers we have spherical 
furrowed grains, as in Dicentra speciosa (fig. 29), where there 
are also some irregularly disposed protuberances ; or Plantago 
media (fig. 30), which approximates somewhat to the irregular 
form of P. lanceolata . Sometimes also we have ellipsoidal 
grains without any apparent furrow, as in Anthriscus sylvestris 
(fig. 31), Adoxa Moschatellina (fig. 32), which is somewhat 
lenticular, Narcissus poeticus (fig. 33), and the very large 
grains of Fritillaria imperialis (fig. 34) and P. Meleagris (fig. 
35). Others again are characterised by being furnished with 
protuberances scattered irregularly over the grains, as Ribes 
aureum and R. fruticosum (figs. 36 and 37), the protuberances 
apparently causing the grains to adhere together in masses. In 
the very minute pollen-grain of Hoteia japonica (fig. 38), there 
is one such protuberance on each side, which is the case also 
with Saxifraga crassifolia (fig. 39). The section of the genus 
* I have Mr. Darwin’s authority for saying that his statement to the 
contrary effect, which will be found in his paper on the species of Primula 
in the “ Journal of the Linnean Society,” vol. x. p. 393, is an error, which 
will he found corrected elsewhere in his writings, and in those of Hilde- 
brand and Lubbock. It has however been copied into several of our text- 
books. 
