92 
OF THE MARINE ALGJ3. 
only whole or perfect specimens ; by which I mean such as 
are provided with the disk by which they were fixed when 
in life, or at any rate with as much of it as possible, in 
order to exhibit the plant’s natural habit. Fragments tom 
off the main stem look very pretty, and do well enough to 
adorn a lady’s album, but, as a rule, are valueless to the 
botanist. In many cases it is absolutely necessary to have 
the entire plant before one’s eyes to determine with cer- 
tainty its place in the system of nature. I will bring 
forward a single example. The genera Callithamnion and 
Phlebothamnion are separated on the ground of the former 
being ‘ corticate ’ — that is to say, furnished with a cortical or 
external integument, which is wanting in the latter. Now, 
there are instances (as I have myself repeatedly ex- 
perienced) where this outer stratum is developed for a 
short space only above the point of attachment, the whole 
of the upper portion of the stem being naked. If, then, the 
student (instead of gathering the whole plant) is contented 
with specimens taken from above the portion invested with 
cortex, how is it possible for him to determine to which 
of the two genera his example belongs, since he has 
deprived himself of the only characteristic mark by which 
they are distinguished ? Much the same may be said of 
the different species of Polysiphonia. 
When, again, the collector comes across Alga? flourishing 
in large tangled groups, he must take care while separating 
them to secure a sufficiency of material for future obser- 
vation. It is a sound axiom in domestic economy that 
frugality applied in the wrong place does but aggravate 
difficulties. And it is as true here as in the more serious 
matters of life. Many a chance of determining the true 
position and natural habit of a plant has been lost from the 
collector having neglected to gather sufficient material on 
the spot and at the right time. A single stem of a Cera- 
mium may perhaps exhibit the generic and specific charac- 
ters sufficiently well ; but, however beautifully laid out, it 
can never set before the eye of the observer the great massy 
