Monthlv Microscopican /I,-, "P nil nit Q^ 



Journal, Feb. 1, IsTO. J ^^^ rOUeil. \JO 



2. Marhings. — 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 Geraniaceie and Camijanulacese is for the 

 most part globular ; but while some of the grains are quite smooth, 

 others are covered with spines; thus the pollen of Camixinula 

 media has a number of short spines sparsely scattered over the 

 surface of the grain, but C. raininmihides is wholly destitute of 

 tliem. In other plants these spines are replaced by tubercles, and 

 both spines and tubercles vary gi'eatly in length and number ; for 

 example, in Valeriana tuherosa the spines are only half the length 

 of those on the pollen of V. montana, the grains being also slightly 

 smaller. The pollen of the Liliaceee is oftened 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. canadense, 

 the grains of the latter species being much more globose and 

 smaller. 



3. Dimensions. — Some instances of the differences observable in 

 the size of pollen-grains have already been published by Professor 

 Gulliver, whose measurements of the poUen of various species of 

 Banunculus show the help that may be derived from this character ; 

 B. arvensis is nearly twice the size of B. hirsutus, their dimensions 

 being respectively ^Irth and gl^th of an inch. 



I have not had the time to make similar careful measurements 

 with the micrometer, but I have seen sufiicient to be satisfied that 

 while there is considerable variation in dimensions between the 

 pollen of one species and that of another, they are tolerably constant 

 in size in the same species. 



For some noticeable differences compare the smaller pollen of 

 Epilobium hracliycarpum with the larger pollen of E. Fleischeri, or 

 that of Senecio gallicns with ^S'. incanus, the spines on the latter 

 species being also much coarser. Again, the pollen of Silene acaulis 

 is but half the size of that of 8. aJjpina, the latter having some 

 beautiful markings in addition ; the pollen-grains of this genus 

 differ from the usual caryophyllaceous type in not having the pits 

 or depressions common in the order, so that the grains become 

 spherical rather than polyhedral. 



4. Colour. — This is not so reliable a character for differentiation 

 as the others noticed, since species differ amongst each other accord- 

 ing to the soil, &c., of the place where they have grown. I remember 

 gathering some years ago, near Ashbom-ne, Derbyshire, a variety 

 of Stellaria Holostea having a dark purple pollen instead of the 

 ordinary pale yellow. An example or two under this head will 

 suffice. 



