414 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 



the gelatine in its immediate neighbourhood be dusted over with pollen-grains of 

 the same plant, in the course of a few hours, as the pollen-tubes are developed, it 

 will be found that they converge upon the stigma in an unmistakable manner. 

 Pollen-tubes, even at so considerable a distance from the stigma as seventy times 

 their own diameter, have been observed to be influenced in this way. Similar 

 results obtain when sections of a style are employed instead of a stigma, but the 

 attraction is not so strong. Isolated ovules laid on the gelatine exert a very marked 

 attraction upon pollen-tubes. In one case as many as forty pollen-tubes were 

 counted converging upon the micropyle of an ovule of Scilla patula. Ripe ovules 

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

 immature ovules are not without influence. 



Noteworthy is the fact that an ovule is found to attract not only pollen-tubes 

 from pollen of the same species, but of others far removed from it in point of 

 affinity. Thus the pollen-tubes of Scilla patula (a Monocotyledon) were found to 

 be attracted by the ovules of Diervilla rosea and Ranunculus acer (Dicotyledons), 

 tubes of Primula sinensis by the ovules of Antirrhinum majus and Digitalis 

 grandiflora, those of Hesperis matronalis by ovules of Lonicera Periclymenum, 

 &c. In these experiments these strange pollen-tubes were 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 accomplished by these 

 foreign pollen-tubes. 



Nor is this attraction limited to pollen-tubes. The delicate hyphse of several 

 mould -fungi are similarly attracted, as also, when the surface on which the ovule 

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

 Termo. 



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

 which exert a chemical attraction upon pollen-tubes, gradually leading them to the 

 micropyle. Though it has not been possible to determine in all cases what these 

 substances are, it is extremely probable that they are of a sugary nature. In the 

 case of plants with chalazogamic fertilization, in which the pollen-tube, as we have 

 seen, never enters the cavity of the ovary, it would be of interest to ascertain if the 

 micropyle is destitute of attraction for pollen-tubes. 



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

 limited to pollen-tubes of the same species, but seems common to pollen-tubes in 

 general, and indeed to fungal hyphae and the like. Thus it happens that instances 

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

 their hyphse down the style to the ovary like pollen-tubes. And so with foreign 

 pollen. Though it is often stated that the pollination of the stigmas of a plant A 

 with pollen from B (a plant not allied to A) is without result, what is actually indi- 

 cated is that no seed has been ripened by the pistil thus pollinated. Experiment 

 has shown that, just as the pollen- tubes of one plant may be attracted towards the 

 micropyle of an ovule of a plant of entirely different family, so pollen will germin- 

 ate on the stigma of a similarly remote plant and form tubes which penetrate 



