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 



