1900] CURRENT LITERATURE 137 
experiment. To acentral disk on the end of a vertical rod are attached six 
radiating arms of strong brass wire, on which are slipped cork disks, and 
to them seedlings are fastened in any desired position. This carrier is 
supported above a circular dish of water into which the roots depend while 
it is rotated on a clinostat. To prevent the retardation of the water as much 
as possible three other glass vessels each about 6™ less in diameter than 
the next outer one are cemented to it, thus dividing the water chamber into 
three concentric spaces 3° wide, in which the rate of movement was practi- 
cally unaffected by the retarding action of the immersed rootlets. 
For rheotropic curvatures roots of Vicia sativa (2-3 long) and maize 
(3-4 long) proved best adapted. Currents varying from 0.8™ per second 
(using a hot air motor) to 0.3™" per second were tried. The lower limit of 
sensitiveness was not reached even at the lowest speed. Curvatures of 
15-35° were obtained in 6 hours and 10-65° in 21 hours with currents of 
0.8-0.3™" per sec., all being positive, z. ¢., against the current. After the 
theotropic curvature has become considerable a counter curvature due to 
§eotropism appears in Vicia sativa, producing a sigmoid form. 
By means of decapitation and covering the root tip with collodion caps, 
Juel sought to determine the receptive region. He concludes that it is the 
growing zone. Whether or not the tip was also sensitive he could not ascer- 
‘ain. Juel is not yet able to decide what factor acts as a rheotropic stimulus, 
and plans to make further researches.— C. R. B. 
W. C. WorspELL © has done most excellent service in bringing together 
the chief views in the vexed discussion concerning the nature of the ovular 
Structures in Coniferae. There is probably no more difficult bit of mor- 
P ology in connection with seed-plants, and the scattered literature of the 
subject needed organization and compact presentation. The problematical 
structures are the so-called seminiferous scale and the sporangial envelope. 
© homologize these structures throughout Coniferae seems to be a well-nigh 
peless task, and a definite solution still remains to be reached. 
is Sdell traces the history of the discussion from Linnaeus (1737) to 
” phol vsky (1897), although its real beginning on the basis of modern mor- 
Scie tid ba Said to date from the announcement of gymnospermy 2 
Celakoy te ie Peaz- The author’s judgment favors the conclusions 0 
axilla rad vies Sees in the seminiferous scale the first two leaves of an 
geek ‘ ae being developed directly in a highly modified form as an out- 
outer soe €bract. Furthermore, each of these two leaves represents an 
at Ot the sporangium, all of the Coniferous megasporangia 
9 
ae ine H. O.: Untersuchungen iiber den Rheotropismus der Wurzeln, Jahrb. 
a Ot. 34: 507-538, 1900, 
of — he structure of the female “ flower” in Coniferae, an historical study. Annals 
"Y 14: 39-82. 1900, 
