INSECTS AND FLOWERS. 
115 
form when magnified 250 diam. Fig. 4 is Luzula campestris , 
nearly spherical, hut with a depressed hand of lighter colour, 
dividing the grain into three nearly equal sections. Figs. 5 
and 6 represent the pollen of plants the mode of fertilisation 
of which is doubtful ; the former is that of the dog’s mercury, 
Mercurialis perennis , elliptical hut quite smooth, and covered 
with very fine reticulations ; the latter of the box, spherical, 
hut with a number of slight protuberances irregularly dispersed 
over the surface of the grain. Plantago lanceolata is described 
by Muller* as having three distinct forms of flower, and he 
suggests that it may be a species in a transitional state from 
anemophilous to entomophilous. It is probable that the form 
of the pollen may also vary. Fig. 7 represents that observed 
by myself, nearly spherical or with badly defined angles, and 
traversed by a single equatorial ridge, with several darker spots 
where the pollen-tubes are emitted. I find the colour described 
in my notes as nearly white, but some of the more perfect 
grains with a deep orange surface, very smooth and shining. 
In figs. 8 and 9 we have the grains of two grasses, the common 
Poa annua , and the “ quaking-grass,” Briza media . The 
spherical form is here somewhat departed from ; but they are 
exceedingly light and smooth. The microscope shows various 
bright spots, which have the appearance of depressions or holes. 
Fig. 10 is the oval perfectly unfurrowed grain of Dactylis 
glomerata. 
In flowers which are fertilised by the agency of insects the 
form and size of the pollen-grains vary to a much greater extent, 
and we find several distinct contrivances for the purpose of 
facilitating their attachment to the legs or bodies of bees, flies, 
and other insects. The most important of these are three : — 
longitudinal furrows varying in number from three to eight or 
nine or even more ; the clothing of the surface of the grains with 
spines or other prominent projections; and the connecting them 
together by means of viscid threads. By far the most common 
form of pollen-grain is ellipsoidal, with three or more longitu- 
dinal furrows. Grains of this shape are obviously more calcu- 
lated to cling to the hairs that clothe the legs and bodies of 
insects than perfectly spherical ones ; while on the other hand 
they would not be so readily carried by the wind. Illustrations 
of such grains with three furrows are afforded by fig. 11, Ra- 
nunculus Ficaria ; fig. 12, Aubrietia deltoidea; fig. 13, Viola 
sylvatica ; fig. 14, Aucuba japonica , in which the anthers 
appear to be filled with an oily fluid ; fig. 15, Lamium album 
(yellow); fig. 16, L. purpureum (red); fig. 17, Nepeta Gle- 
choma (white); fig. 18, Platanus orientalise fig. 19, Conval- 
laria Polygonatum ; and fig. 20, Bryonia dioica . 
* “ Befruchtung der Blumen durch Insekten,” p. 342. 
