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Show CHAP. I. INTRODUCTORY REMARKS. 24 k S f these causes of error will al o have struc . on1e o . l .1. . t d b the seeds ha Vln o· b en allow c to been e 1m1na e Y bb · 1 t 1 · . te on bare damp sand, and Ing p an In pgea:umsi n· af or 1't 1. s n ot ll''I-~oly that ill-matur d and well.- matu;ed or diseased and healthy s eds, would ger~l-nate at 'e xac tlY the saine time · The s.a me r. ult will h been gained in the several cases l n ' hich only a fe~;eof the tallest, finest, and healthiest plants on each side of the pots were measured. Kolreuter and Gartner* have proved that with ~ome plants several, even as many as from ~~ty .t sixty: pollen-grains are necessary for the ~ rt1hsati n f ~11 · 1 the ovules in the ovarium. N aud1n als f nnd .1n 1 the case of Mirabilis that if only on r two of Its very large pollen -grains were placed n the stigma, the plants raised from such s eels w re dwar!ocl. I was therefore careful to give an amply sufficient supply of pollen, and generally co:ere 1. th stigma with it; but I did not take any spec1al pa1ns to place exactly the same amount on the stigmas of the se~ffertilised and crossed flowers. After having actecl In this manner during two seasons, I rememb r d that Gartner thought, though without any direct vid ne~, that an excess of pollen was p rhap injurious ; and 1t has been proved by Spallanzani, Quatr fag s, and l N ewport,t that with various animals an exce s f the seminal fluid entirely prevents fertilisation. !~ was · therefore necessary to ascertain wh ther the fert1hty of the flowers was affected by applying a rather smal~ and an extremely large quantity of pollen to the stigina. Accordingly a very small mass of poll n-grains was * 'Kenntniss der Befruchtung,' 1844, p. 345. Naudin, 'Nouvelles Archives du Museum,' tomt . 'i . p. 27. . h' 1 Transactions Ph1losop lCa Soc.' 1853, pp. 253-258. CHAP. I. INTRODUCTORY REMARKS. 25 placed on one side of the large stigma in sixty-four flowers of Ipomcea purpurea, and a great mass of pollen over the whole surface of the stigma in sixty-four other flowers. In order to vary the experiment, half the flowers of both lots were on plants produced from selffertilised seeds, and the other half on plants from crossed seeds. The sixty-four flowers with an excess of pollen yielded sixty-one capsules; and excluding four capsules, each of which contained only a single poor seed, the remainder contained on an average 5 · 07 s~eds per capsule. The sixty-four flowers with only a l~ttle pollen placed on one side of the stigma yielded Sixty-three capsules, and excluding one from the same cause as before, the remainder contained on an average 5 ·129 seeds. So that the flowers fertilised with little pollen yielded rather more capsules and seeds than did those fertilised with an excess; but the difference is too slight to be of any significance. On the other hand, the seeds produced by the flowers with an excess of pollen were a little heavier of the two ; for 17 0 of them weighed 79 · 67 grains, whilst 170 seeds from the flowers with very little pollen weighed 79 · 20 grains. Both lots of seeds having been placed on damp sand presented no difference in their rate of germi~ation. We may therefore conclude that my experiments were not affected by any slight difference in the amount of . pollen used ; a sufficiency having been employed In all cases. The order in which our subject will be treated in the. present ~olume is as follows. A long series of expenment~ will first be given in Chapters II. to VI. rabies Will afterwards be appended, showing in a COndensed form the relative heights, weights, and fertility of the offspring of the various crossed and self-fertilised |