1910] CURRENT LITERATURE 159 
amples of reversion to remote ancestral characters rather than as results of recent 
hybridization.” —J. M. C. 
Comparative leaf anatomy of Agave.—In a genus consisting of species so 
incompletely characterized and so hard to differentiate as those of the succulents 
usually are, every applicable character is valuable and its application is a real 
service to science. Little beyond the most general and scattered facts have here- 
tofore been recorded for the histology of Agave, and a recently published study 
of its leaf anatomy, by MULLER,* therefore, stands alone on the shelves. The 
difficulty of such a study and the value of its outcome are as largely influenced 
by the accuracy of naming and the representative character of the material on 
which it is based as on fulness of representation. In the present case the large 
collections of Palermo and La Mortola, where many of the species are planted 
out in the open, furnished material which is as likely to have been normal and 
accurately named as could be hoped for in the genus Agave, and its examination 
seems to have been carefully and systematically made. The details of structure, 
which are rather fully illustrated by means of drawings and low-power photo- 
’ Sraphs, are followed by an analytical key occupying five quarto pages, and yet 
it is doubtful whether tenable names are likely to be found for many plants by 
its aid—W. TRELEASE. 
Death by low temperature.—Using the molds, Aspergillus, Penicillium, and 
Botrytis, BarteTzKo has made a new investigation under the guidance of PFEFFER, 
on death by cold.t* He finds these fungi able to bear temperatures in a sub- 
cooled solution (without actual freezing) which would be fatal in the same time 
were the solution allowed to freeze. But even in the sub-cooled solution death 
ensues on longer exposure. With increase in the osmotic pressure of the plant 
Sap there is a lowering of the death point, but there is no simple relation between 
the two. Isotonic solutions of different sorts have nearly the same effect on the 
resistance of the plant to cold. Only with Aspergillus niger did the use of a 
potassium nitrate solution reduce the resistance notably. In contrast to the con- 
clusion of Motrtscu, BarTETzKO thinks death by cold cannot be due merely to 
withdrawal of water, because in certain cases this will be borne, while in others 
death takes place above the temperature at which any considerable loss of water 
occurs.—C. R. B. ’ 
. 
Root excretions.—Inasmuch as the minuteness of the quantity of root excre- 
tions has again and again prevented the determination of the kind of acid, other 
than H.CO;, whose presence the corrosion experiments have led observers to 
ania, 
*S MOLLER, Cart, Beitrage zur vergleichenden Anatomie der Blatter der Gattung 
Agave und ihrer Verwertung fiir die Untersoheidung der Arten. Bot. Zeit. 67':93- 
139. pls. 4, 5. figs. 22. 1909. 
‘4 BARTETZKO, Huco, Untersuchungen iiber das Erfrieren von Schimmelpilzen. 
Jahrb. Wiss. Bot. 47257-0908. 1909. 
