52 
biosa. There are, besides, other natural orders where similar 
variety occurs. 
But differences of form are met with in plants of the 
same genus, by which the one species or the other is readily 
marked off by its pollen ; thus the pollen grain of Anemone 
sulphured is roundish, but that of Anemone montana is 
elliptic ; the pollen of Aronicum Doronicum is much more 
elongate than that of A. scorpioides; and while the grains 
of Ranunculus philonotis are round and yellow, those of 
R. platanifolius are elliptic, white and smaller. 
2. Markings. Here again there is endless diversity, and 
a boundless field lies open for the researches of tired-out dot 
and line hunters of diatom- valves. A few instances only of 
the more striking differences can be given here. 
The pollen of the Geraniacece and Gampanulacece is for 
the most part globular, but while some of the grains are 
quite smooth others are covered with spines ; thus the pollen 
of Campanula Media has a number of short spines sparsely 
scattered over the surface of the grain, but C. rapuneuloides 
is wholly destitute of them. In other plants these spines 
are replaced by tubercles, and both spines and tubercles 
vary greatly in length and number ; for example, in Vale- 
riana tuber osa the spines are only half the length of those 
on the pollen of F. montana, the grains being also slightly 
smaller. The pollen of the Liliaceoe is often covered with a 
more or less prominent reticulation, which is subject to 
much variation ; compare, for example, the coarse network 
which invests the pollen of Lilium croceum with the finer 
reticulation of L. eanadense, the grains of the latter species 
being much more globose and smaller. 
3. Dimensions. Some instances of the differences obser- 
vable in the size of pollen grains have already been pub- 
lished by Professor Gulliver, whose measurements of the 
pollen of various species of Ranunculus show the help that 
may be derived from this character ; R. arvensis is nearly 
