26 
POPULAR SCIENCE REVIEW. 
formed calculated for an enduring term of life, are represented 
by ferns, horse-tails, club-mosses, and all flowering plants. 
Among cellular plants, the lowest place is generally assigned to 
the group of algae, though the lowest forms of fungi are equally 
elementary in their structure with the lowest forms of algae. 
To give a concise technical description which shall draw the 
line between algae and fungi is not easy ; and indeed, as we 
shall see presently, the two groups overlap at several points. 
Several well-marked characters which hold good in the large 
majority of cases, may, however, be mentioned. Algae and 
fungi agree in being “ Thallophytes,” i.e. in the fact that they 
do not in general show any differentiation of their parts into 
distinct stem and leaves ; they differ, however, in the locality 
in which they are found, algae being generally water-plants 
(either fresh or salt) or, if not, growing at least in very damp 
places, while fungi are aerial plants, and very commonly para- 
sites. A more important distinction is that algae almost 
invariably form chlorophyll, the green colouring matter on the 
presence of which depends the power of the plant to decompose 
the carbonic acid of the atmosphere (or of the air dissolved in 
fresh or salt water) and hence to carry on an independent exist- 
ence ; while fungi never form either chlorophyll or starch, 
and hence have no power of independent existence, but live as 
parasites or epiphytes on either living or decaying vegetable 
or animal substance. In sea-weeds, however, it is very common 
for the chlorophyll to be overlaid and obscured by some other 
colouring material — red, brown or purple. The mode of repro- 
duction is, as we shall see, extremely variable. 
The division of the great group of algse into orders is 
attended with great difficulties. One of the most easily under- 
stood systems of classification, though not in all respects satis- 
factory, recognises three orders, recognised by the colour of 
their tissues and spores; viz. (1) Rhodosporese or Floridese, 
with a leaf-like or filamentous rose-red or purple, rarely brown 
or greenish-red thallus, and red spores ; (2) Melanosporese or 
Fucoidese, with a leaf-like, shrubby, cord-like, or filamentous 
thallus of olive-green or brown colour, and dark spores ; and 
(3) Chlorosporese or Confervoidese, extremely variable in form, 
and often microscopic, with green spores. Of these, the plants 
belonging to the first two orders are almost exclusively marine, 
while those belonging to the third chiefly inhabit fresh water. 
It will be our object to examine them more in detail, and 
mainly in respect to their microscopic structure and the 
physiology of their reproduction, rather than in relation to the 
mode by which the families or species can be distinguished from 
one another. 
1. Taking these orders according to their grade of organisa- 
