103 
quotes the fact that the generic importance of nervation in leaves 
was first discovered by the study of fossil types, whereas the bot- 
anist frequently concerns himself so entirely with the mere form 
of the leaf that his figures and descriptions are frequently of no 
value to the palzobotanist. Another point, and an important one 
from the geological standpoint, is that the correct determination 
of a genus is of small importance compared to the exact descrip- 
tion and portrayal of the specimen, the vital point being that 
these shall be so exact that there shall be no doubt as to the 
identity of a type wherever it may again be found. These criti- 
cisims might well be carefully considered by all who are engaged 
in descriptive work. 
In describing the methods which should guide in the study 
of geologic correlation by means of fossil plants, a plea is made 
for as wide a comparison as possible with foreign forms, which 
are frequently transitional, and thus avoid such an error as was 
made in the case of our Laramie flora. The importance of tab- 
ulating the species of plants common to separate areas of sup- 
posed identical strata is urged and such a table of distribution 
is given for the plants in the Triassic areas of the United States. 
Act 
Silva of North America, Vol. III. Anacardiacee—Leguminose. 
Charles Sprague Sargent. (4to. pp. 141, Plates XCVIII- 
CXLVII). 
The trees described and illustrated in this volume of the Silva 
are as follows: Cotinus Americanus, Rhus Metopium, Rhus 
typhina, Rhus copallina, Rhus vernix, L. (R. venenata, DC.), 
Rhus integrifolia, Eysenhardtia orthocarpa, Dalea spinosa, Rob- 
inta Pseudacacia, R. Neo-Mexicana, R. viscosa, Olneya Tesota, 
Ichthyomethia piscipula, Cladrastis lutea, Sophora secundifiora, 
S. affinis, Gymnocladus dioicus, Gleditsia triacanthos, G. aquatica, 
Cercidium floridum, C. Torreyanum, Parkinsonia aculeata, Py 
microphylla, Cercis Canadensis, C. Texensis, Prosopis jult — 
P. pubescens, Leucena glauca, L. pulverulenta, Acacia Farnesiana, 
A. Wrightii, A. Greggti, Lysiloma latisiliqua, Pithecolobium 
Unguis-cati, P. brevifolium and P. flexicaule. 
Rhipsalis Regnellii, n. sp. G. A. Lindberg. (Gartenflora, 
XXXix. 118-124, figs. 31, 32.) 
