1883.] 



MICROSCOPICAL JOURNAL. 



191 



the feet of the base spread out, when 

 it is complete. The figure renders 

 further description unnecessary, as the 

 stand is exceedingly simple in design. 



The Development of Pleuro 

 coccus. 



BV THE EDITOR. 



More than a year ago Mr. F.Wolle, in 

 the course of private correspondence, 

 stated that the common Pkurococcus 

 — the pulverulent, green alga, found 

 everywhere on old fences, tree-trunks, 

 etc. -^ was a stage in the growth of 

 Ulothrix. The evidence in support 

 of this statement, however, was not 

 given, and we are still unacquainted 

 with the observations upon which it 

 was based. At the time, we endeav- 

 ored to cultivate the plant, and induce 

 it to take on a filamentous growth, but 

 all our efforts in this direction failed. 

 The unicellular condition persisted, 

 and we were forced to the conclusion 

 that the only way to follow the devel- 

 opment of the plant was to watch it in 

 its native habitats at all seasons. 



On the fourth day of February, this 

 year, when the weather was very mild 

 and ice was melting rapidly, we found 

 some Pleurococciis on moist rocks in 

 Central Park. On examining it care- 

 fully many of the cells were observed 

 to be taking on a filamentous form of 

 growth. This was the first time we 

 had seen any such tendency manifested 

 by the plant, and the discovery was a 

 surprise. 



The cells of the Pkurococcus varied 

 in diameter from 5.8 ju (.00023") to 10.8 

 ^(.00041") or even II jU. If we except 

 the presence of a distinct gelatinous 

 envelope, which surely does not exist 

 in our specimens, the species corres- 

 ponds to P. angulosus. The filament- 

 ous plant consisted of a series of near- 

 ly square cells measuring about 7.25 n 

 (.00028") in diameter. It agrees with 

 Ulothrix compacta tolerably well, and 

 we have given it that name. 



The conclusion from these observa- 

 tions strengthens the position which 

 Mr. WoUe has maintained for several 

 years, and which he has expressed 



quite recently, in a letter, in these 

 words : " I reason from analogy and 

 say that all the forms of Pkurococcus, 

 Protococcus, Chlorococcus, Ghvocapsa, 

 etc., belong to, and are mere develop- 

 ing forms of, higher algae. I have had 

 such positive evidence of transforma- 

 tions I cannot think otherwise." 



Kirchner, a very accurate and ex- 

 perienced observer, says: "The 

 genus Protococcus contains a number 

 of heterogeneous forms of which cer- 

 tainly the most, if not all, are develop- 

 ing forms of higher alga^, as copulating 

 microspores, resting macrospores, or 

 products of a peculiar disintegration 

 of filamentous plants, as noticed by 

 Cienkowski." 



We are are not quite prepared to 

 accept the conclusions thus indicated, 

 even from such high and respected 

 authorities. It cannot be said that the 

 conclusions are fully supported by ob- 

 servation. Very many of the unicel- 

 lular plants are known to pass through 

 different stages, and to propagate in- 

 definitely without, so far as we yet 

 know, assuming a higher, or in anywise 

 more complex, stage of existence. It 

 seems hardly proper to generalize free- 

 ly concerning a subject of which com- 

 paratively so very little is known. We 

 are prone to be conservative about it, 

 for the reason that it is in strict ac- 

 cord with the system of the develop- 

 ment of plant and animal life in the 

 world, that there should be a certain 

 number of alga^ which have never ad- 

 vanced beyond the most primitive 

 condition of cellular life. While it is 

 true that some unicellular forms have 

 been observed to develop into higher 

 plants, we have no means of distin- 

 guishing between a true spore — a 

 product of some process of propaga- 

 tion of a filamentous plant having the 

 strange potency to reproduce its pa- 

 rent form, — and its prototype, which 

 never advanced beyond the unicellu- 

 lar stage ; as the ovum, in its earliest 

 stages, is to the eye the same, whether 

 it encloses the germ of bird or beast 

 or man. Surely we must have some 

 forms of plant-life that have not ad- 

 vanced beyond the condition of a 

 primitive cell. 



