773 LECTURE XLIII, 



in the various tubes. Only the mere reference can here be made to the complicated 

 processes, combined in fact with cell-divisions, which Strasburger describes in the 

 pollen-tubes of the Gymnosperms. 



The inference from these statements, apparently so obvious, may seem 

 to be contradicted again by other facts. In the first place by the fact that the 

 oosphere itself already possesses a cell-nucleus, with nuclein in it, before fertilisa- 

 tion, and in the conjugation oS.' Spirogyra it is expressly stated by Schmitz and 

 Strasburger that the nuclei of the two conjugating cells simply fuse with one 

 another, and Strasburger has demonstrated the same in other cases also. When 

 therefore it comes to answering the question, what kind of substance is transferred 

 to the oosphere as fertilising material, we must allow that the question is not 

 yet sufficiently answered by the observations named. As a hypothesis it may in 

 the meantime be assumed that the nuclein of the two sexual cells is not alike in 

 constitution, and that the nuclein of the male cell thus carries into the oosphere 

 something other than it already possesses. Meanwhile we must leave the problem 

 here shortly treated of in this incomplete form. 



One of the most surprising facts connected with the reproductive processes 

 is the action at a distance, or mutual attraction of the two sexual cells towards one 

 another. I select this expression for the facts to be examined because it is short 

 and at least clearly denotes the matter ; though the words ' action at a distance ' 

 and ' attraction ' are not to be understood in exactly the same sense as in physics. 



In the numerous descriptions given by observers as to the behaviour of the 

 antherozoids in the neighbourhood of the oosphere, and of swarming gametes 

 and even of antheridia in the neighbourhood of oogonia, we meet almost without 

 exception with most definite expressions of the fact that a certain mutual interaction 

 of the sexual cells at a certain distance exists, and this always of such a kind 

 that the union of the two cells is thereby accomplished or promoted. This process 

 is the more remarkable because immediately after fertilisation has been accomplished 

 this mutual attraction has disappeared. 



From a large number of such cases I will take a few only, as follows. 

 Speaking of the fertilisation of the Ferns, and especially of that of Ceratopteris 

 thalictroides, so favourable for observation, Strasburger says {'Jahrb./ur wiss. Bot.' 

 vii., p. 402) :— 



'If a prothallium with ripe sexual organs is laid in water, the antheridia 

 usually open first, and in favourable cases the archegonia soon after. In the case 

 of Pteris serrulata one has nevertheless to wait probably about half an hour or 

 more on the average; with Ceratopteris thalictroides, however, rarely more than 

 twenty minutes. 



The antherozoids, which at first come by chance near the apex of the arche- 

 gonium, just as near other foreign bodies, here behave very curiously as soon 

 as the neck has opened. The instant they meet with the slime in front of 

 the canal their movement becomes slower ; it is seen that they are here held 

 back and their movements impeded by a resistent medium. Some remain fixed 

 m the sUme, some succeed in freeing themselves and hurry away: in most cases 

 however, neither of these events occurs, but the antherozoid is so directed 

 by the slime poured radially out of the canal that it steers, apex forwards, 



