ON TIIE MODE OF GROWTH OF SOME OF TIIE ALGyE. 
3 
both in the same genera and species, and at different phases in 
the same species, still in some the form it assumes is very con- 
stant for the same phase of its life, particularly in some species. 
Thus, in Spirogyra (fig. 8), it enables us to distinguish the 
plant at once, because it assumes the form of a spiral band 
attached to the inner surface of the cell-wall, giving it an 
exceedingly beautiful appearance. In some confervoids, it is 
more or less stellate. In the mature cells of the larger Drapar- 
naldise (fig. 2; a green branching seaweed-like plant, adhering 
to stones in running streams), it is disposed in a band round 
the equator of each cell. In many the contents are granular, 
in some homogeneous, or of uniform consistence. The number 
of cells in a single plant varies from one up to many hundreds ; 
indeed, as they are all derived from one by its division con- 
stantly, there is really no limit, except such as imposed by the 
time required for it, and by the change of external circum- 
stances, such as the seasons bring, which check the progress of 
that particular phase. 
The most remarkable phenomena of the freshwater algae are 
those which are concerned with the multiplication and the 
reproduction of the species. Broadly, it may be said that every 
cell of an alga is capable of living, growing, and multiplying, if 
separated from its neighbours. Still, nature has so arranged 
that there are cells frequently more especially devoted to this 
end ; and there are times in its life when the process more dis- 
tinctly goes on. In order to understand these processes, let us 
for a moment notice the mode in which this process takes place 
in the true algae, or seaweeds. In these is to be found the 
representative of that mode of fertilisation adopted in the higher 
orders by means of pollen. Now it will be remembered that 
when the pollen-grain (fig. 3, a) falls upon the moist end of 
the style, namely, the stigma, it produces from certain parts 
small delicate tubes. These tubes (fig. 3, b, b) penetrate the 
substance of the style, passing between their cells (fig. 3, c, c ) 
to ultimately reach the ovule, or future seed. Acted upon 
by it in some unknown way, the latter becomes fertilised, and 
ultimately ripens into the matured seed. 
Now, in the true algae, the representatives of the pollen are 
called “ antherozoids.” Each consists of a very minute cell, 
having one or two fine hairs, or cilia, spring from one end, or 
one from each end (fig. 4). These cilia have the power of moving 
in a screw-like manner, whereby the cell is propelled. In the 
common bladderwrack of our coasts, the process may be readily 
observed on the bulbous ends of the fronds. If a thin section is 
made, cavities opening on the exterior will be seen to have been 
divided. Placed under the microscope in water, branches (fig. 
5, a) may be seen springing from the wall of the cavities, the 
VOL. vi. — NO. XXII. c 
