318 BOTANICAL GAZETTE [OCTOBER 
Pollen tube of Houstonia. MATHEWSON”? has studied the advance of the 
pollen tube in Houstonia, coming to the conclusion that any mutual influence 
between the tube and the cells with which it comes in contact is very slight; 
and that the direction of the advance of the tube seems to be chiefly in response 
to a stimulus originating in the egg apparatus, perhaps in the egg itself —J. M. C. 
Operculina.—Housr?3 has published a synopsis of the genus Operculina 
as the second paper of his series on North American Convolvulaceae. It com- 
prises about twenty tropical species, which are perhaps better known to many 
botanists under Convolvulus and Ipomoea. In North America fifteen species 
are recognized, two of them being described as new.—J. M. C 
Influence of temperature upon flowering of fruit trees.—Ecologists and 
physiologists will be interested in the phenological notes presented by SANDSTEN** 
relative to the influence of temperature and other factors upon the time of flower- 
ing of certain fruit trees. He reaches the conclusion that “physiological constants 
can be formulated from the climatic conditions during the ten months preceding 
the time of flowering.” —E. Mrap Wixco 
Effect of light on growth.—SrLpy?s has extended the work of MacDoucaL 
‘to include four other species, mostly those which are latex-bearing. MacDov- 
GAL’s conclusions that light does not have a retarding influence on growth and 
that it does stimulate ph acre processes in the meristematic tissues are 
confirmed.—RaymonD H. Pon 
Varieties of roots developed by English ivy.—Miss RanpoxPx’? finds that 
Hedera Helix may be induced to form in all seven kinds of roots according to 
the conditions of moisture —RAymonpD H. Ponp. 
22 MaTHEWsoN, C. A., The behavior of the pollen tube in Houstonia coerulea. 
Bull. Torr. Bot. Club 33:487-493. figs. 3. 1906. 
23 House, H. D., Studies in the N. Am. Convolvulaceae. Il. The genus Oper 
culina. Bull. Torr. Bot. Club 33: 495-503. 1906. 
24 SANDSTEN, E. P., Conditions which ota os time of the annual flowering of 
fruit trees. Bull. Wisc. Exp. Sta. 137: 1-21. 
25 SELBY, A. D., Studies in etiolation. Bull. Torr. Bot. Club 34:67-75- P poet 
figs. 4. 1906. 
26 DOLPH, Harriet, The influence of moisture upon the formation of roots 
by cuttings of ivy. Bull. Torr. Bot. Club 34:93-09. figs. 4. 1906. 
