26 



FKESn-WATER ALGJ^ OF THE UNITED STATES. 



The (Icvclopnicnt of the distinguisliing threads of the coUema out of the ordmary 

 nostoc-ccll has never been confirmed by any other observer ; but it seems to me 

 that it must be at least provisionally accepted, although De Bary expresses some 

 doMbt of it. {Morphol. und Physiol, der Pdzc, FlecJdcn, &c., p. 290.) 



The researches of M. Baranetzky were directed to the developing of a nostoc 

 out of a collema. Hicks and other observers had previously stated that they had 

 seen this, but none of them had given sufficient details as to the method of their 

 observations, to be fully convincing. 



M. Baranetzky placed sections of actively growing fronds of CoUema pidposum, 

 Ach, upon smooth, damp earth, using all proper precautions to prevent external 

 influence. After some days the sections became less transparent and intensely green 

 from the crowding of the gonidia, which were noAV arranged in curved rows closely 

 rolled together into balls. Upon the upper surface of the section appeared little 

 gelatinous balls or warts, which contained gonidia in rows, and gradually developed 

 tyincal nostoc forms, whilst on the edges of the sections appeared little colorless 

 wart-like masses of jelly, in which, after some time, appeared gonidia, some of 

 which developed into the typical nostoc form, others into true collemoid plants. 



Mr. Baranetzky further states that he watched the body of the section gradually 

 change by the continual growth and increase of the rows of gonidia, before alluded 

 to, and by the disappearance of the collemoid threads, until at last the whole 

 mass of the tissue of the lichen had been converted into a true nostoc, which was 

 finally identified as Nostoc vesicnrium, D. C* 



I have no observations of my own to offer upon this subject; but think enough 

 has been done to show not only that the nostocs proper have very close relations 

 with the collemoid lichens, but that they are probably a peculiar phase in their 

 life-history. This being the case, it may seem a perfectly superfluous work to 

 indicate species amongst the nostocs. To any one who has given much study to 

 the fresh-water algfe, the reply t(? this Avill immediately suggest itself; namely, that 

 in tlic present state of the science it seems impossible to avoid it; they are so 

 commonly thrust at one by collectors, amateurs, &c., are so distinct, are so often 

 the subject of tongue and pen, that tliey must have a name. The idea that at- 

 taches to the term species is at present not a very definite one; that there are, 

 however, amongst the nostocs fixed forms, which do not change into one another, 

 and can readily be distinguished, I have no doubt. Such forms are herein de- 

 scribed. If they be only life stages of lichens, I have no doubt that it will finally 

 be found that each so-called species of nostoc has its own peculiar so-called species 

 of lichen, from which it alone springs, and into which alone it can develop. It 

 seems to me, then, that as yet no cause for abandoning the specific names of the 



* In order to aid any one desirous of going over tliis sulijcct more thoroughly, a list of papers is 

 appended: — 



Yentenab und Cassini Opuscula Phytolog., 1817, vol. ii. p. 3G1. 



Dr. Hermann Itzigsohn. Botanische Zeitung, 18.54, p. .521. 



Prof. Julius Sachs. Botanische Zeitung, 18.55, p. 1. 



Bayrhoffcr. Botanische Zeitung, 1857. 



Hicks. Journal sf Microscopical Science, ISCl, ]). 90. 



Baranetzky. Bulletin de la Socicte des Sciences Xat., St. Petersburg, vol. xii. p. 418. 



