1897] POLYMORPHISM IN THE ALGAE 113 
form; and hence in all work on such algae this line of investigation 
demands the greatest attention. 
If in the future the lower algae are investigated on the lines 
I have indicated, it will be possible for us to emerge from the 
confusion prevailing at present, and to bring the study of these 
organisms on to a higher plane. Such investigations will, according 
to my view, be of very great value in advancing the systematic know- 
ledge of species, not only because they will enable the cycle of forms 
belonging to a given species to be completely determined, but also 
because in the diagnosis of the species they will enable new charac- 
ters to be recognised. The way in which the various stages in the life- 
history of a lower organism react to external conditions, especially 
the way in which its reproduction depends upon the external world, 
furnish specific characters as important_as the morphological ones. 
And these physiological characters become so much the more 
valuable in proportion as the external characters become less con- 
spicuous. In the bacteria we have already been compelled to take 
such characters into account; and the time is not far distant when 
it will be self-evident that in the diagnosis of a new alga, there 
must be placed alongside of the accurate description of its structure 
and the history of its development, a clear account of its behaviour 
in relation to the external world. To-day the mere determination 
and the giving of a name to a species is far too generally the 
sole aim in systematic botany, and it is here, among these lower 
organisms, that the proper goal of the systematic knowledge of 
plants may be soonest reached—to present a complete picture of all 
the peculiarities of each several organism. 
The whole of my more recent experiments with algae confirm 
my earlier experience, and correspond with the results of the in- 
vestigation of bacteria and fungi—they show, namely, that within 
the time available for experiment, the hereditary characters of an 
organism are not markedly altered by external conditions. The 
variations in size, form, cell-structure, and reaction to external 
influences, oscillate within definite limits—limits which up to the 
present we have not been able to pass. The constancy of the species 
meets us with striking clearness in all cultivations and experiments 
under existing conditions; it remains for further experiments, carried 
on for longer periods, and with the aid of better methods, to decide 
whether these limits cannot be broken through. The important 
observations on certain bacteria, in which it was found that heredi- 
tary characters such as virulence and pigment-production, could be 
suppressed for a long time, point in this direction. But anything 
like such a result has not hitherto been obtained among the algae, 
although it is possible that it may be obtained in the future. 
In spite of the actual constancy of specific character among the 
