* 
110 BOTANICAL GAZETTE [ AUGUST 
missible to depart from priority in cases of names which have clearly arisen 
through gross geographic errors on the part of their authors, as for instance, 
Asclepias syriaca L. (which comes from the United States), and Leptopetalum 
mexicanum Hook et Arn. (from the Liu-Kiu Islands.) 
12. Hybrids are designated by the names of the parents directly con- 
nected by the sign X, the alphabetical order of the specific names being 
maintained, e. g., Cirstum palustre X rivulare. \n the position of the names 
no-distinction is made as to which was the father and which the mother plant. 
To hybrids we consider the binomial nomenclature unsuited. 
13. Manuscript names have no right under any circumstances to consid- 
eration on the part of other authors, not even when such names appear upon 
the printed labels of exsiccaté, The same thing holds in the case of horticul- 
tural names or designations in trade catalogues. The recognition of species 
presupposes a printed diagnosis, which it is true may occur even upon a label 
of exsiccati. 
14. An author has no right to alter at will a once published generic or spe- 
cific name, unless moved to do so by very weighty reasons, such as those in 
Rule 11. 
Signed by A. Engler, I. Urban, A. Garcke, K. Schumann, G. Hieronymus, 
P. Hennings, M. Giirke, U. Dammer, G. Lindau, E. Gilg, H. Harms, P. 
Graebner, G. Volkens, L. Diels. 
B. L. Rospinson, Cambridge, Mass. 
A CONVENIENT POTOMETER. 
THE most satisfactory method for the demonstration and exact 
measurement of the amount of water taken up by transpiring plants or 
by branches is by the use of the potometer. The simplest form is that 
used by Darwin and Phillips.’ Practical instruments have been 
described by Kohl, Detmer, and others. A modification of Kohl’s 
apparatus, designed in this laboratory, has been found to meet all the 
requirements of exact measurement, and at the same time is useful in 
demonstration in the lecture room, where its operations may be wit- 
nessed by a class of eighty or one hundred without difficulty. For the 
latter purpose the apparatus is always ready for use and may be fitted 
with a plant in five minutes. 
The apparatus consists essentially of a horizontal tube of 1” inter- 
nal diameter, calibrated into portions containing 100™ of water. At 
* DARWIN, Physiology of Plants, 73. 1894. 
