10 W. B. TURNER, FRESH-WATEB ALGM OF EAST INDIA. 



by form alone. The advocates of chlorophyll-systematizing, if they are logical, will partly 

 return to Ehrenberg's views, and absorb Penium within Closterium; this would not be 

 nearly so objectionable as bringing, as they often do, most heterogeneous forras into close 

 ;i | iposition. 



To raeet varions objections, and to deal with plants having lateral chlorophvll, 

 Lundell in 1871 proposed certain new subgenera. Under Cosmarium he gave n. sub-gen. 

 Pleurotceniopsis ; and under Staurastrum the n. sub-gen. Pleurenterium; hut what hetero- 

 gen}' is thus created! In the first we find C. ovale Ralfs, C. striolatum (Näg.) Arch., 

 and C. elegantissimum Lund.; and under the latter we have such forms as Stan. (/rande 

 Bulnh., S. Brasiliense Nokdst., and S. sexcostatum Bréb. ') The only deduction 1 can 

 make is that the suggestions of the distinguished author, altliough verv ingenious, are 

 quite unworkable'. 



It is not for me to be hypercritical, and that chlorophyll arrangement (of which we 

 know but too little,) is of high value I freely admit, but would any Algologist discard a 

 distinctly lunate form from Closterium because it was found to have irregular chlorophyll- 

 masses in place of the usual fillets? A knowledge of the cell-contents is as necessary to 

 perfect understanding of the plant, as is a correct idea of the cell-form, but I submit 

 (with extreme deference to many high authorities) that, in our present state of knowledge, 

 we find it of more specific than generic value, i. e. so far we can confidently base ideas 

 of classification upon it. I do not say that the advocates of classifying by cell-contents 

 are wrong, I only suggest that their views are too advanced, and hence inconvenient for 

 present practical use. Wallich, Desra. Beng. p. 185, says, »aecording to the varying 

 periods of growth of the organism, the endochroine may be equably disposed in minute 

 granules throughout the protoplasmic cell-contents, it may be aggregated into definitely 



or indefinitely shaped masses, or it may present itself in the form of radiating bands 



aecording as the granules have remained dispersed or have coalesced under the molecular 

 law to which they are subject. In some genera the disposition of the endochroine must 

 no doubt, be regarded as highly characteristic, as, for instance, in Docidium, Penium. 

 Tetmemorus, and Closterium. But even in different individuals of each of these genera. 

 and in the same individual under different conditions, it will be found to vary greatly.» 

 In considering these remarks it must not be forgotten that they were written 32 years 

 ago; still that they contain much truth is undeniable. To the same point tend Archer's 



critical remarks on Pleurotcenium, (1868) »He would not contend against the genus, 



but was not prepared to adopt it.» 



Cceteris paribus, a classification by form is much more easily followed than a scheme 

 of more elaborate construetion; and it had been my intention, in this little dissertation, 

 to have arranged all my Desmid-forms as nearly as 1 could in form-sequence, but, from 

 long-eontinued sickness which delaved my work, I have been compelled to abandon the 

 idea. However, I liave appended to the principal genera outlines of sub-genera based 

 solely upon external form, as I deem such the safer guide to a practical arrangement ol 

 these plants. 



') Can any Desniids possess much raore dissiniilar forms than these? 



