154 BOTANICAL GAZETTE [AUGUST 
mination.” The genus is limited, as is usual now, to those abietinous forms in 
which both shoots and leaves are dimorphic. A somewhat full discussion of the 
value of the histological characters often used in classification reaches the con- 
clusion that they have no greater intrinsic value than any other characters, being 
useful but not infallible guides, likely to vary more than some other 
The two great divisions proposed are TENUISQUAMAE (with relatively thin cone- 
scales) and CrassISQUAMAE (with cone-scales notably thickened toward the 
apex). Under the former are the sections Strobus (10 spp.) and Cembra (3 spp.); 
under the latter the sections Integrifoliae (8 spp.), Serratifoliae (4 spp.), Indicae 
(3 spp.), Ponderosae (12 spp.), Filifoliae (7 spp.), Cubenses (5 spp.), Sylvestres 
(ro spp.), and Pinaster (11 spp.). A useful feature of the contribution is a chron- 
ological list of specific names, extending from 1753 to 1903. The author’s long 
study of the genus makes this contribution unusually rich in facts and sugges- 
tions.—J. M. C 
TRANSEAU*} has made a preliminary announcement of certain results in 
connection with the investigation of the causes of xerophily in bog plants. Using 
Rumex Acetosella, great modification in the appearance and structure of the 
leaves was produced by varying the conditions; for example, growing in moist 
conditions and in dry sand. Also, the marked xerophilous characters induced 
by growth in the latter substratum were also obtained by growth in an undrained 
wet sphagnum substratum of low temperature. Further, under these conditions 
the drops of oil or resin, characteristic of bog xerophytes, were formed in the 
epidermis and in the cells adjacent to the bundles. He concludes that these 
modifications in the case of the bog habitat are a response to the unfavorable 
conditions for absorption by the roots, due to low temperature and lack of aera- 
tion. It is also suggested that the development of palisade tissue in = 
to strong light is correlated with drouth rather than with light, resulting i” 
increased transpiration. ‘The elongated palisade cells, therefore, are an 
tation for the ready transfer of food materials in the leaf tissues, under the stress 
of a reduced water supply.”—J. M. C : 
HABERLANDT in reexamining the perceptive mechanism of heliotropi¢ pst 
finds three types:?4 (x) those in which the lamina alone is sensitive; €. £5 Beg es 
discolor and probably shade plants in general; (2) those whose lamme an a 
are perceptive; e. g., Tropaeolum spp., Malva verticillata (fide VocHtING) reas 
probably climbing and twining plants; (3) those whose petioles or motor pee 
are sensitive; ¢. g., Phaseolus. He suggests that in euphotometric foliage © 
the cells of the upper epidermis constitute a sensory epithelium for the perception 
of light. Sometimes all cells share alike in this function, but in some Po 
certain cells are specialized, forming a more localized sense organ- ; 
. U def e 
*3 TRANSEAU, E. N., On the development of palisade tissue and resinous 
In leaves. Science N. S. 19:866-867. 1904. 
Jatt. Ber- 
ANDT, G., Die Perception des Lichtreizes durch das Laubb 
ERL 
Deutsch. Bot. Gesells. 22:105-119. pl. 8. 1904. 
Pea 
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