326 BOTANICAL GAZETTE [OCTOBER 
‘vegetation on the moraine deposited by the last ice sheet; (2) a forest of 
birch and hazel; (3) a layer of arctic-alpine plants, occurring down to sea 
level in Shetland; (4) a forest of pine, hazel, and birch, occurring up to 3200 — 
feet; (5) a layer of peat, accumulated from stage 4 to the present day, con- 
sisting entirely of moorland plants. This means an alternation of two forest 
beds with two arctic beds, before the peat came in.— oe 
The structure of Mesoxylon.—In 1910, Scorr and MAsLen published 
Mesoxylon as a new genus of Cordaitales, which included five species. One 0 
these, M. Sutcliffii, has now been studied by MASLEN,” so far as the structure 
of stem and leaf is concerned. The name of the genus refers to the fact of 
its intermediate position between Cordaites and Poroxylon, and the known 
species appear to bridge the gap almost completely. The present study con- 
resemblances of M. Sutcliffii to each of these genera, and also its differences 
in each case. One of the most interesting features of Mesoxylon is that it 
illustrates the gradual extinction of centripetal wood and the establishment of 
endarch structures in the Cordaites.—J. M. C 
The chromosomes of Dahlia.—Isuikawa* finds 16 and 32 chromosomes 
in Dahlia coronata, but 32 and 64 in nine other species and races. In the pollen 
mother cells of D. coronata in the heterotypic prophase, the chromosomes are 
paired, but in the other species the pairing is seen also at the homotypic 
mitosis, indicating, according to IsHIKAWA, that the vegetative cells of these 
species are tetraploid. 
rom the literature and his own observations, the reviewer has tabulated 
the number of chromosomes in more than 30 species of composites, and finds 
that the number varies from 3-6 in Crepis virens to 21-42 in Hieracium flagel- 
lare, with 8-16 or 9-18 as the most usual numbers. The extraordinary variety 
of form in Compositae may be related to the variation in the chromatin.— 
CHARLES J. CHAMBERLAIN. 
teolytic enzyme of Drosera.—The proteolytic enzyme of four species 
of Drosera (D. auriculata, D. Menziesii, D. peltata, D. Whittakeri) has been 
investigated by Miss JEAN Wutre,’s who finds a pepsin-like enzyme present 
in all of them, but unassociated with any peptolytic or tryptic enzyme. 
Peptic digestion occurred either in acid, basic, or neutral medium, every test 
giving a good biuret reaction for peptones; but in no instance could the 
faintest trace of amides be found with the tryptophane reaction. This dis- 
23 Masten: Artur J., The structure of Mesoxylon Sutclifii (Scott). Ano. 
Botany 25: 981-414. pls. 33-36. 1 
pl os oneness M., Cytologische Getic iiber Dahlien. Bot. Mag. Tokyo 25:1. 
ae a 
se — The proteolytic enzyme of Drosera. Proc. Roy. Soc. London 
B 83: 14159. 
