INFLUENCE OF THE ORIGIN OF THE CELLS ON FERTILISATION. 905 
Fncus platy carpus^ &c.) the reproductive cells of the same plant are not so closely 
related, and especially where fertilisation is caused by actively or passively motile 
antherozoids, there being at least a possibility of their meeting with oospheres of 
more remote origin. Even in Vaucheria, where the antheridium is the sister-cell of 
the oogonium, the curving of the former, and the direction in which the antherozoids 
escape, 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 Dioecism, 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 Fucacese, in some Saprolegnieae and Characeae {Nitella syncarpa, &c.), in 
many Muscinese, in the prothallium of many Ferns {Osmunda regalis) and of most 
Equisetaceae, 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 Moncecism, is also 
common in the vegetable kingdom, as in some Algae, many Muscinese, 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 (Edogonium produces both male and female 
cells, the same Vaucheria-^2imQw\, 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 of Bryuni) 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 Kölreuter (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-fertilisation of a flower or of an individual. 
