198 THE ORCHID REVIEW. [JULY, 1915. 
A special interest attaches itself to these primitive Algz, for in them 
we can trace the very origin of the sexual process, while behind them may. 
be seen the still more primitive organisms in which the only method of 
reproduction is by the vegetative process of cell bipartition. The 
introduction of sexuality has been followed by a whole series of progressive 
modifications to meet the requirements of changing conditions, culminating 
in the highly specialised processes met with to-day, while the primitive 
method of reproduction by vegetative division has taken an 
increasingly subordinate position, without, however, being lost where its 
retention served any useful purpose. 
A hurried glance through the progressive stages of sexual specialisation 
in different groups will indicate more clearly what has taken place. At the 
outset we find plants consisting of a single cell, and propagating them- 
selves by vegetative division. Then follow others where the cells remain in 
contact, forming filaments or tissues, but propagating themselves in the 
same way. The two Algez already considered show the beginning of the 
sexual process, while a third, @idogonium, makes another step in advance. 
Here the sexual cells are perfectly differentiated, and instead of’two, 
similar conjugating zoospore-like. gametes we find a small moving, 
spermatozoid and a large resting ovum. Both partners are still on 
equal terms as regards the union of their nuclei, but the female cell remains - 
in connection with the vegetative body of the parent, and alone assumes the 
duty of accumulating food-supplies for the next generation. Still higher, 
in Coleochete, the odspore, as the fertilised cell is called, divides up into 
a group of cells, in each of which a zoospore is formed, thus indicating 4 
certain analogy with the formation of the sporogonium, or spore-mother, in 
the simplest liverworts. 
This brings us to the next great division, the Bryophyta—liverworts and 
mosses—which have become adapted to an aerial mode of existence, and 
show a marked alternation of generations. The plant-body consists either 
of a thallus-like tissue ora stem and leaves, in either case on reaching 
maturity producing the sexual bodies in specialised organs, the male called 
antheridia and the female archegonia. The latter are flask-shaped bodies, 
formed of cellular tissue, with a tubular neck, and bearing the ovum at 
the base. Fertilisation is still by ciliated bodies, called spermatozoids, 
which are produced within the antheridia, and are carried down to the 
archegonia by rain or dew, and on reaching the neck of the latter ar 
attracted to it and pass down its mucilaginous canal to the ovum, which it 
fertilises. The fertilised. ovum now develops into the so-called moss-fruits 
which produces spores asexually, these falling on some damp place and 
germinating, giving rise to a new moss-plant—the sexual generation. It 1S 
noteworthy that these plants in some cases produce exclusively male OF 
