Deck. 31, 1909 The Queensland Naturalist. 9T 
or vegetative condition. Later on. if the conditions are 
favourable for the production of fruit (technically known 
as spores), the mass loses its bright green colour, and changes 
to a dirty brown, or yellovdsh-browm ; it becomes dis- 
organised to all apjiearance ; separate threads can nO' 
longer be drawm out, or only a few' which still remain in 
the sterile state ; and the whole mass seems to have become 
a soft, pulpy substance that falls to pieces through the 
fingers, as though in an advanced stage of decomposition.. 
It is, how'ever, at this time, that the heart of the collector 
is filled with joy at the sight. This repulsive-looking 
substance is the Spirogyra in fruit, and maybe he has visited 
that pool a dozen times, in as many weeks, in anticipation 
of that sight, and on each previous occasion found the 
species he washed to determine obstinately flourishing 
literally “ like the green bay tree,” in wdiich vegetat:ve 
state — as remarked already — a final determination of the 
species can rarely be made. Thus much for the plants 
as they appear to the unassisted sight. The rest must 
be revealed only by the aid of the microscope, for w'hich 
purpose a one-inch objective is highly suitable for making 
all general observations : while a higher power, a one-sixth 
or one-eighth inch is to be preferred for taking dimensions, 
as giving greater accuracy, for the dimensions are one of 
the most important factors in the determination of species. 
Viewed through a microscope then, the green sterile 
threads of Spirogyra become objects of exquisite beauty. 
They consist of cylindrical cells of various length, united 
end to end, sometimes wdth a plane partition as in Figs. 
4 to 15, in other species with the membrane of each cell 
curiously folded back like a hat with the crown crushed 
down (see Fig. 1 to 3). Upon this distinction the genus is 
divided into tw'o sections. The cylindrical cell-w^all is as 
transparent as the clearest glass, and has a pleasing lustre 
that is probably due to the coating of mucilage, in which 
it is enveloped, and to which is due its slippery feeling wUen 
handled. Within the transparent cell are one or more 
beautiful green spiral bands, turning (generally wdth great 
regularity) from right to left, and applied close to the inner 
surface of the cell- wall. The edges of the spiral bands 
are generally delicately notched or toothed ; the density 
or laxity of the turns of the spirals varies much even in the 
same species. I have frequently observed that w^here 
the plants have an abundance of fresh w'ater. as when caught 
and held in a briskly flowing stream, the spirals are dense 
and the cells short ; while the same species, growing in 
stagnant and polluted w'ater, exhibits lax sj^irals and long 
cells, and hence it apjiears that these characters are of 
little value specifically, but are mere indication of the vigour 
of the plant, in the majority of cases. In making my ob- 
servations, I have in nearly every species been able to get 
