INFLUENCE OF THE ORIGIN OF THE CELLS ON FERTILISATION, 905 



''ucus platycarpus, &c.) the reproductive cells of the same plant are not so closely 

 related, and especially where fertilisation is caused by actively or passively motile 

 Jantherozoids, there being at least a possibility of their meeting with oospheres of 

 pnore remote origin. Even in Vaucherta, where the antheridium is the sister-cell of 

 |the oogonium, the curving of the former, and the direction in which the antherozoids 

 jscape, indicates that fertilisation does not usually take place between the contiguous 

 organs, but between those more remote or even between those produced by different 

 individuals. The tendency for fertilisation to occur only between reproductive cells 

 of as remote relationship as possible within the same species is manifested in a great 

 variety of contrivances, the simplest being that on each individual of the sexual 

 generation only male or only female organs are produced. Thus between the two 

 uniting reproductive cells there lies the entire course of development of the two 

 plants when the plants are derived from the same mother-plant, and a still longer 

 course of development when they are derived from different mother-plants. This 

 distribution of the sexes, which is generally termed Dicecism, occurs in all classes 

 and orders of the vegetable kingdom, showing that it is a useful contrivance for the 

 maintenance of different species. Thus we find this phenomenon in many Algae, as 

 in most Fucaceae, in some Saprolegniese and Characeae {Nitella syncarpa^ &c.), in 

 many Muscineae, in the prothallium of many Ferns {Osmunda regalis) and of most 

 Equisetacese, and in many Gymnosperms and Angiosperms. 



If the plant which produces both kinds of sexual organs is large or at least 

 highly differentiated, distance in the relationship of the two kinds of reproductive 

 cells is still attained by the male and female organs being produced on different 

 branches ; and this phenomenon, which is in general termed Monoecism, is also 

 common in the vegetable kingdom, as in some Algae, many Muscineae, and a very 

 large number of Gymnosperms and Angiosperms'. 



But another condition which, according to the law just stated, should appa- 

 rently be very unfavourable, is also of very common occurrence in the vegetable 

 kingdom, namely, that the reproductive organs are in close contiguity, and the sexual 

 cells are therefore of near even if not always of the closest affinity. Thus, for 

 example, the same cellular filament of CEdogonium produces both male and female 

 cells, the same Vaucheria-&i2imQn\. antheridia and oogonia in close proximity, the same 

 conceptacle of Fucus platycarpus produces both oogonia and antheridia ; the 

 carpogonia of most Characeae are produced close beside the antheridium on the same 

 leaf; the archegonia and antheridia of some Mosses (species oiBryum) are collected 

 together in hermaphrodite receptacles, the prothallia of many Ferns produce both 

 kinds of reproductive organs side by side ; in the flowers of Angiosperms herma- 

 phroditism is the typical and most common arrangement. But in all these cases 

 where the aim is apparently to favour the union of sexual cells nearly related to one 

 another, there are at the same time contrivances which hinder the male cells from 

 reaching the contiguous female cells ; or at least to render it possible that this 

 should not always happen. This fact was first recognised by Kolreuter (1761) and 

 Karl Conrad Sprengel (1793), and has been further illustrated recently by Darwin, 



^ The arrangement of the reproductive organs termed Polygamy is also a contrivance intended 

 to hinder perpetual self-fertilis-ation of a flower or of an individual. 



