•iU V-KinntlZATION AND FORMATION OF KIUHT IN VHANKR0QAM8, 



the gelatine in itvs iuii\>oiUato neighbourhood be dustotl ovor with poUea-grdns of 

 the same plant, in tlie coiu-se of a few hours, as tlie pollou-tubi>8 aw deWopad, it 

 will be found that thoy oonvorge upon tlie stigma in an unmistakable miumer, 

 Pollen-tubos, ovou at so considerable a distance froi\» the stigma as s«>\"mty iAwm 

 tlieir own iliaiwotor, havo been observed to be influenood in tliis way, Siiailar 

 resvilts obtain wluvn sections of a stylo are omployed instead of a stigma, but tho 

 attraction is uot so strong-. Isolated ovuloa laid on the gelatine esort a voiy mai'ked 

 attraction upon polloa-tubea. In ono caso «*< many aa forty pollen-tubes wwe 

 counted converging upon tlie micropyle of ai> ovule of l^ioltlii, paiuhu Eipe ovules 

 ready to be fertilized exert the strongest attraction, though younger and as yet 

 iuvnjftture ovules ai-o not without inlluence. 



Noteworthy is tlio fact that an ovule is found to attract not only pollea-tubes 

 from pollen of the same spoi-ios. but of otliei's far ivu\ovod from it in point of 

 affinity. Thus the poll on- tubes of SdUa paivia (a Monocotyledon) wore found to 

 be attracted by the ovules of Dieroilla ivma and KaituwemJ-iw mw (Dicotyledons), 

 tubes of Primula s'mtmm» by tlie ovules of AnUrrhiwum mtt^m nod JDigiiteiw 

 grandijlora, those of //espam matronalis by ovulos of Lonioera P«noly<inmMm\ 

 &;o. In these experiments these strange pollen-tubes wei-e not only attracted 

 towards the micropyle, but actually in a few cases penetrated it. Still, no suggestion 

 is made that anything of the nature of fertilization could be aooomplislwd by tliese 

 foreign pollen-tubos. 



Nor is this attraction limited to poUen-tuboH. The delicate liyphro of soveviil 

 mould-fungi are similarly atti-acted, as also, when tlie surface on whioli tlxo ovwle 

 rested was moistened, was that common micro-organism of decomposition, Baokfiuw, 

 Termo, 



Thus it appears that substances are present in the stigma, style, and ovules, 

 which exert a chemical attraction upon pollen-tubes, }j;mduMlly loading tliom to tlie 

 micropyle. Though it has not boon possible to detoinuitio in all oases what these 

 substances are, it is oxtromoly probable that they are of a sugaiy nature. In the 

 case of plants with clialazogamio fertilization, in which the poUon-tubo, m we have 

 seen, never enters the cavity of the ovary, it would ho of interest to asoovtain if the 

 micropylo is destitute of attraction for pollen-tubes. 



As stated, the attraction exerted by a givon ovule or portion of a pistil is not 

 liniited to pc)lloii-tid)0H of tho himuo species, but hooiiih common to poUon-tubes in 

 general, and indeed to fungal hyphee iu\d the like. Thus it happens that instances 

 are recorded in which fungal spores fell on tho stigma, and germinating there, sent 

 their hyphro down the nlyio to tlio ovary like pollen- tubes. And so with foreign 

 polloii. Though it is often atatod that the poiliiwiliion of the stigmas of a plant A 

 with pollen froiri ii (a plant not iiiliod to a) is without ivnult, what is actually indi- 

 cated is that no seed Iimh boon ripened by tlio pistil thus pollJiuited, Experiment 

 has shown that, just m the pol](<n-tubes of ono pliiriit may bo attracted towai'ds the 

 micropylo of an ovule of a phmt of ontiroly did'oronli fauiily, so pollen will gormin- 

 ate on tlio stigma of n, Hiiriilarly roniote plant and form tubes which penetrate 



