Bibliographical Notices. 137 



same. In Conjugates the spores germinate, and by the development 

 of the first shoots produce a new individual, but in the Desmidiece 

 (at least as indicated by Closterium*) and Diatomacea, the repro- 

 ductive bodies, which in the former case often assume forms alto- 

 gether at variance with those of the perfect plant, and in both are 

 generally of a very different size, appear rather to be contracted 

 fronds which, without any actual germination, by the mere produc- 

 tion of articulations produce new individuals. And hence in specific 

 discrimination it is absolutely necessary to know the whole of the 

 phases through which a species passes, exhibiting great varieties of 

 size and form, before it is possible to determine what are specific 

 characters and what are not ; and thus many a puzzling appearance, 

 which was before quite inexplicable, becomes clear and instructive. 



Mr. Ralfs however holds, and we believe rightly, that the mode of 

 production of the cells in some other tribes of Alga? ultimately fol- 

 lows the same type. 



" In the Desmidiea" he says, " the multiplication of cells by re- 

 peated transverse division is full of interest, both on account of the 

 remarkable manner in which it takes place, and because it unfolds, as 

 I believe, the nature of the process in other families, and furnishes 

 a valuable addition to our knowledge of their structure and physio- 

 logy- 



" The compressed and deeply constricted cells of Euastrm offer 

 most favourable opportunities for ascertaining the manner of the di- 

 yision ; for although the frond is really a single cell, yet this cell in 

 all its stages appears like two, the segments being always distinct, 

 even from the commencement. As the connecting portion is so 

 small, and necessarily produces the new segments, which cannot 

 arise from a broader base than its opening, these are at first very 

 minute, though they rapidly increase in size. The segments are 

 separated by the elongation of the connecting tube, which is con- 

 verted into two roundish hyaline lobules. These lobules increase in 

 size, acquire colour, and gradually put on the appearance of the old 

 portions. Of course, as they increase the original segments are 

 pushed farther asunder, and at length are disconnected, each taking 

 with it a new segment to supply the place of that from which it has 

 separated. 



" It is curious to trace the progressive development of the new 

 portions. At first they are devoid of colour, and have much the ap- 

 pearance of condensed gelatine, but as they increase in size the in- 

 ternal fluid acquires a green tint, which is at first very faint, but soon 

 becomes darker ; at length it assumes a granular state. At the same 

 time the new segments increase in size and obtain their normal 

 figure ; the covering in some species shows the presence of puncta 

 or granules ; and lastly, in Xanthidium and Staurastrum the spines 



* See Morren's memoir in the 5th volume of the Second Series of ' An- 

 nates des Sciences Naturelles.' A second mode of propagation appears to be 

 indicated by Mr. Haifa at tab. 27. In other Desmidiece the development 

 of the spores has we believe not been yet ascertained, but from analogy we 

 believe that it will prove similar to that of Diatomacea. 



