1906] CURRENT LITERATURE 155 
revision, and investigations of the cytological phenomena involved are especially 
needed. PascHer’s observations were microscopic to be sure, but he has appar- 
ently attempted no cytological observations at all—R. THrESsEN. 
Sigillarian stems.—Owing to the rarity of sigillarian stems showing structure 
the description of new specimens is of particular interest to paleobotanists. 
IDsTON’® has given a well-illustrated and adequate description of Sigillaria 
elegans, which differs from the historic S. Menardi in that the primary wood of 
the former is continuous instead of broken up into bundles. The protoxylem is 
external to the metaxylem, and both are composed of scalariform tracheids. 
The secondary wood is about equal in thickness to the primary, and shows medul- 
lary rays which are mostly one cell thick and one to nine cells high. The outer 
margin of the primary wood is crenate, and from the furrows arise the leaf traces, 
of which there are about twenty-eight in a cross section; these do not seem to 
possess any secondary wood. As is usual in sigillarian stems the pith, phloem, 
and inner cortex have perished, and the outer cortex contains a broad zone of 
periderm. . elegans, with a continuous ring of primary xylem, S. spinulosa, 
with a mixture of continuous and discrete xylem, and S. Menardi, with separate 
bundles, form a good series, and judging from the scanty data available it seems 
that this series represents a sequence in time. The features of S. elegans support 
the view that the genus sprung from forms more like Lepidodendron.—M. A. 
CHRYSLER. 
Mycoplasmic propagation of grain rust—Erixsson has published another 
instalment of his studies on the demonstration of the propagation of grain rust 
by means of mycoplasm, this time dealing with Puccinia graminis.?° Four means 
are recognized by which the uredo stage of the rust may possibly arise in spring 
time in winter wheat: (1) from spores of the barberry aecidium, which in turn 
arose from the resting teleutospores that had remained dormant over winter; 
(2) direct infection of the wheat plant from the resting teleutospores (homoecism); 
(3) uredo infection from mycelium remaining alive in the wheat plant over winter; 
and (4) from endogenous germs of disease (mycoplasm) which pass the winter 
in a resting condition in the live wheat plant. He marshals a large array of data, 
drawn from his own observations and experiments and from a wide range of 
literature, to show that the first method, although it exists, is by no means uni- 
versal, that the second is highly probable, that the third never occurs in northern 
regions, if anywhere, and that the fourth is the most common method everywhere. 
Although the conclusions of the author will not be accepted by most investigators 
of this difficult problem, yet the array of data is interesting. Two clearly drawn 
gans of Brongniart’s 
19 Kipston, RosBeERT, On 
Histoire des végétaux jossiles. Trans. mele Soc. as 4r: 533-550. pls. 1-3. 
1905. 
a9 > ERIKSSON, JaKop, Ueber das vegetative Leben der Getreiderostpilze IV: 
nia graminis Pers. in der heranwachsenden Getreidepflanze. Kungl. Sy. Vet.- 
tay Handl. 395:1-41. pls. I, 2. 1905. 
