DXTBLIN KATVBAL HI8T0BT 80CI1STT. 207 



The following paper was directed to be printed in the "Proceedings,** 

 the lateness of the hour having prevented its perusal : — 



NOTICE OF SOME CASES OF ABNORMAL GROWTH IN THE DESMIDIACEJS. 

 BY WILLIAM ARCHER. 



It has occurred to me that the accompanying sketches, representing 

 an abnormal mode of growth in the Desmidiacea?, exhibiting, as they 

 do, an appearance so curious and unusual, might possess some interest 

 for the students of that family. I am aware that, in Mrs. Herbert 

 Thomas's interesting communication ('* Quarterly Journal of Microscopical 

 Science," vol. iii., Plate V., Figs. 17 and 18), that lady has figured a 

 very similar case in Cosmarium margaritifemm to that shown in my 

 drawing of Stattrastrum defectum; yet I have thought it might be worth 

 while to figure some examples of the phenomenon still farther carried 

 out in other genera, although it may be quite possible that even more 

 curious aberrations may have been met with by other observers. 



^The first case of this mode of malformation to which I shall direct 

 attention is a monstrosity of & Yanctj of Mtcrasterias Jenneri — (Plate I., 

 Fig. 9). Here the intervening growth, produced after the mode which 

 prevails in the Pesmidiaceaj, between the two older segments of the 

 original frond, and which, in the normal condition, ought to have formed 

 two new segments, forms a somewhat quadrate expansion, but has not 

 assimied any definite outline. "We find it within filled with endo- 

 chrome, similar to the parent segments, to about the dimensions of one 

 of which it has attained. It is about the simplest form of the irregu- 

 larity under consideration which I have to bring forward ; the interven- 

 ing new portion forming only an irregular, shapeless growth. 



I here wish to draw attention in passing to the form itself (Fig. 9), 

 a fair idea of which in the normal state can be obtained by imagining 

 the irregular central growth as absent, and the two older segments in 

 apposition. It will be seen that this variety agrees with Micrasterias 

 Jenneri (Halfs) variety /3, in the superficial granules being somewhat 

 large, giving a somewhat dentate or roughish appearance to the margin, 

 but it differs from both varieties, a and y3, by its lateral lobes not being 

 bipartite, and of course wanting their emarginate subdivisions. Thus, 

 if Mr. Ralfs justly called this species, both a and y3, puzzling, the draw- 

 ing before us exhibits a form even more so. On account of the lobes 

 not being incised, as just pointed out, this form (of course I need 

 not repeat that I do not allude now to its abnormal irregularity) 

 becomes, I think, likely to be mistaken for an Euastrum, to which genus 

 it closely approaches through £. ohlongum. Nor is the resemblance 

 lessened by there occurring occasionally specimens with the incisions 

 between the segments, not linear, and, therefore, the lobes not closely 

 approximate, but spreading and sinuously lobed. However, the absence 

 of any inflations, when viewed laterally, as well as the want of a termi- 

 nal linear notch, though there is a slight concavity or depression at 

 the ends, whilst the lobes are cuneate and more radiant, exclude this 

 form from Euastrum. I would here, then, take the opportunity to 

 characterize this plant thus : — 



