474 BOTANICAL GAZETTE [JUNE 
of these two types with respect to the arrangement of the leaves. The Hun- 
tingdon elm (U. vegeta), commonly believed to be a hydrid, produced 732 
opposite-leaved seedlings and 239 alternate-leaved, the expected Mendelian 
result if the Huntingdon elm is an F, hybrid between U. glabra and U. mon- 
tana. Other ratios given by different varieties were 245:95 and 310:84, 
when the parent trees had grown in such situations that their pollination was 
probably effected by pollen from the same variety. The progeny of a “Jersey” 
elm, which was probably pollinated by U. montana, consisted of 17 opposite- 
leaved and 1g alternate-leaved, equality probably being “expected.” The 
“English” elm (U. campestris) is also an undoubted hybrid, but this rarely 
produces fertile seeds, though an abundance of samarae are produced; 19 
boxes of seeds of the English elm gave no germinations. This sterility and 
also the appearance of many imperfect flowers in the various cultivated 
varieties are accepted by the author as additional evidences of hybridity. 
The author believes that the varieties produced in genera having a number of 
species are of fundamentally different nature from those in genera including 
a single species. In birch, oak, lime, poplar, and willow, as in elm, the varieties 
are hardly to be distinguished from distinct species except by breeding tests. 
They are generally the result of hybridization, while in the beech and the ash, 
each of which is represented in northern Europe by a single species, the nu- 
merous varieties are of the nature of “sports,” whose relationship and varietal 
value are recognized at once, as in the case of cut-leaved, purple-leaved, 
weeping varieties, etc—Gro. H. SHULL 
Geotropism.—ZIELENSKI,® working in Jost’s laboratory, has made accu- 
rate determinations of presentation, reaction, and critical times, and of the 
relaxation index in geotropism, using the roots of Lupinus albus and Lepi- 
dium sativum. Use of the clinostat and horizontal microscope renders his 
clinostat from end of exposure to beginning of reaction). “Critical time 
is the least exposure that is not entirely nulled by an opposite and imme- 
diately following exposure of equal length (organs are on a horizontal equally 
rotating clinostat after the second exposure). ‘Relaxation index” is the ratio 
of the length of the equal individual rotation periods to the length of equal 
individual exposures (shorter than presentation time), that will not result : 
F ‘ ne 
summation. Reaction, presentation, and critical times were determ! 
*) ZIELENSKI, FELIX, Ueber die gegenseitige Abhangigkeit geotropischer —_— 
momente. Zeitschr. Bot. 3:81-101. 1911 
