468 BOTANICAL GAZETTE [DECEMBER 
time in the work under review, but they are all brought together here, and so 
focus our attention on the ninety (about) specific names (considerably over one- 
half) that bear ARTHUR’s name as their authority; and he is also responsible 
for sixteen (about one-half) of the genera. However, he is not quite so extreme 
in this respect as MuRRILL has been in his monograph of the Polyporaceae. 
ARTHUR has obtained part of his genera from new material and part by splitting 
up old genera, basing the new genera largely upon their possession of one or more 
of the O, I, II, III stages characteristic of the rusts. His familiarity with the 
rusts is such that he is able apparently, if given only the II stage, to tell what other 
stages it possesses, and so can place it in a genus. 
Judging from this past tendency to publish new species under the old recog- 
nized genera, a tendency he has not yet entirely lost, I expressed doubt to the late 
Professor UNDERWOOD, editor of the Flora, that ARTHUR would follow his Vienna 
paper in his treatment of the North American Uredinales. As he did follow it, 
however, I promptly received from UNpERWooD the following: “Some time ago 
you charged that ARTHUR was not possessed of the courage of his convictions in 
regard to his publication of genera in the Uredinales. I commend to your prayet- 
ful attention the second part of Vol. VII of North American flora, issued March 6, 
and move that it is time to have a retraction of that charge.” I herewith publicly 
make that retraction; but what will become of this nomenclature when some 
ambitious name-juggler revises our rusts fifty years hence, or possibly even after 
the next botanical congress!—G. P. CLINTON. 
NOTES FOR STUDENTS 
Turgor and osmotic pressure.—The relation between these stands in great 
need of accurate study. LEPEsCHKIN, a few months ago, discussed the matter 
before the German Botanical Society.2 After reviewing the terminology, he 
designates as turgor and turgescence the condition of tenseness of the tissues due 
to internal pressure in the cells. For quantitative purposes he defines as Zz 
turgor pressure (Turgordruck) the total pressure exercised by “cell contents’ 
upon the ‘‘cell walls;” but he evidently means by Zellinhalt the cell sap, for he 
explains that the Zellwdnde must be of plasmatic nature. By turgor tension 
(Turgordehnung) he designates the elastic elongation of the walls in any dimen- 
sion, wrought by turgor pressure. This only partly accords with the best usage 
in this country, where turgidity rather than turgescence names the condition, 
and turgor the internal pressure which produces turgidity, while turgor tension 
has seldom been considered quantitatively. LepEscHKIN then analyses turgor 
pressure into four components: (a) surface tension (Zentraldruck), vatying 
between 0.016 and 1.6 atmospheres, with a variation of 10-12 per cent.; () j 
swelling of the plasma (Quellungsdruck); (c) the osmotic pressure of substances = 
dissolved in the plasma; and (d) the osmotic pressure of the cell sap and the wall 
? Lepescukin, W. W., Ueber den Turgordruck der vacuolisierten Zellen. Ber. 
Deutsch, Bot. Gesells. 26a: 198. 1908. 
