Marcii 1, 1870.] 



HARDWICKE'S SCIENCE-GOSSIP. 



53 



other is readily marked off by its pollen ; thus the 

 pollen-grain of Anemone sulphurea is roundish, but 

 that of Anemone montana is elliptic ; the pollen of 

 Aronicum Boronicum 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 Geraniacetc and Campamdacecc 

 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. rapunculoides 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 

 Valeriana tuberosa 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 

 Liliacea is often covered with a more or less promi- 

 nent reticulation, which is subject to much varia- 

 tion: 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 differ- 

 ences observable in the size of pollen-grains have 

 already been published 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 twice the size 

 of R. hirsutus, their dimensions being respectively 

 sjs and g^ 8 of an inch. 



I have not had the time to make similar careful 

 measurements with the micrometer, but I have seen 

 sufficient to be satisfied that while there is consider- 

 able 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 bracJiycarpum with the 

 larger pollen of E. Fleischeri or that of Senecio 

 gallicus 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 S. 

 alpina, 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 according to the 



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

 remember gathering, some years ago, near Ash- 

 bourne, Derbyshire, a variety of Stellar/a Holostea 

 having a dark purple pollen instead of the ordinary 

 pale yellow. An example or two under this head 

 will suffice. 



The pollen of Ajuga genevensis is yellow, but that 

 of A. pyramidalis is usually white ; again, while the 

 grains of OrnitJiogalum umbellatum are large and 

 yellow, those of 0. nutans are small and white. 



Some objection may be raised to any reliance 

 being placed upon the dry shrivelled-up grains of 

 herbaria specimens, such specimens being in most 

 cases the only ones obtainable for purposes of 

 investigation ; but the structure of pollen is such as 

 to bring into greater prominence the pores, folds, 

 valves, and other markings which are met with on 

 their surface alter the grains have collapsed by the 

 discharge of their contents. 



In regard to the mounting of these objects for 

 the microscope, they show to the best advantage 

 when put up perfectly dry : the cells should be 

 sufficiently shallow to admit of no more than a 

 single layer, and at the same time deep enough to 

 permit the grains to move about. If pollen is 

 mounted soon after it has been discharged from the 

 fresh anthers, the fovilla is apt to condense on the 

 covering glass, and the slide soon becomes useless. 

 The stamens taken from an unopened flower-bud 

 furnish the best and cleanest pollen, and these 

 should be selected in preference to those taken from 

 the fully-developed flower. 



Canada balsam, glycerine, and other media are 

 occasionally helpful in making out structure ; thus 

 the pores of Campanula rotundifolia, Phyteuma 

 Halleri, and other allied species, are made much 

 more distinct when mounted in balsam. 



FLORAL FINDINGS. 



HAD you allowed my little introductory note to 

 appear when you published "Floral Find- 

 ings," the Pylades and Orestes of Science-Gossip 

 could not have attacked me. 



I also find that a third valiant knight of the quill 

 takes up his pen this month to shoot hard words at 

 me. Ey, gentlemen, fy ; go find " a foeman worthy 

 of your steel." 



All I can say is, that I fear the trio are sadly 

 wanting in the gift they credit me with, — " imagi- 

 nation," or else they must have caught my mean- 

 ing at a glance. I never thought that any one could 

 suppose I intended to say that I had gathered the 

 plants contained in my flower-basket at this season 

 of the year, or had really arranged them in a real 

 vase. 



It has long been a habit of mine to bring home a 

 bunch of " Eloral Findings," sort them at leisure, 

 and jot down all I know or remember reading about 



