MORPHOLOGY OF MEMBERS. 
act is always that two cells of the simplest possible kind combine, either completely 
coalescing with one another, or at least their contents becoming partially inter- 
mingled so as to afford a starting-point for a fresh development. It is the 
essential characteristic of sexual reproductive cells that each is incapable of 
further development by itself, this being the result of the combined action of 
two such cells. 
It is only in the lowest forms of vegetable life, in some Algae and Fungi, 
that the two cells which take part in the act of sexual union are alike or at least 
very similar in size, form, and physical properties. In this case their union is 
called conjugation, and the cell capable of germination which results from the 
union a zygospore. In all other cases the two uniting cells are strikingly different 
in size, form, and physical properties. In these cases one of the two cells, 
the male cell, conveys to the other only a very small quantity of material by 
means of which it produces an effect upon it ; this other cell, the female cell, 
contains by far the largest proportion of the material which takes part in the 
development incited by the act of union. With the exception of a few complicated 
cases among Algae and Fungi, which will be particularly described, the relation- 
ship between the two sexual reproductive cells is still more clearly indicated 
by the fact that the male cell is motile, carrying to the other cell the fertilising 
material The motion of the male cell is however of two kinds ; it may either be 
spontaneous, as in most Cryptogams, when the cell is termed an anther ozoid^ ; 
or, as in Phanerogams, the male cell, then called a pollen-grain, becomes detached 
from the parent-plant, and conveys the fertilising material to the female cell first 
of all by the aid of external forces, then by its own growth. The female cell, on 
the other hand, which is fertilised by means of the male cell, remains at rest at 
the place where it was formed, or at most, as in the Fucaceae, is carried about 
passively; with the exception of the cases above referred to it is always a naked 
primordial cell, and is termed the oosphere, or germinal vesicle. After fertilisa- 
tion, it secretes a cell- wall, and is then termed an oospore; from this, either at 
once, or after a period of rest {resting spore), the young plant is subsequently 
developed. Some not inconsiderable deviations from this plan will have to be 
pointed out in the class Carposporeae of Thallophytes ; but even in these cases 
the essential condition of fertilisation remains, that the male cell only incites to de- 
velopment, while the development itself proceeds entirely from the female organ. 
Very considerable variety is shown in the morphological characters of the 
sexual organs, if we take a comparative view of the whole vegetable kingdom ; 
but in the larger groups of plants we find the morphology of these organs to agree 
completely in all essential points, even when the anatomy of the vegetative organs, 
the habit and mode of life of the plants that compose them, vary greatly. When 
considering, in Book II, the distinguishing characteristics of the different classes 
of plants, our attention will be specially directed to the morphology of the sexual 
organs, and it will be sufficient here, as an introduction to what follows, to define 
the most general terms connected with these organs. 
' [The term ' antherozoid' was first proposed by Derbes and Solier, Ann. des sc. nat. 1850, vol. 
XIV. p. 263.] 
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