DEFENSES OF COCK-SPUR THORN. 
303 
the wind or a passing animal,* but this is probably not the case 
with KneifRa. 
In the limited time and space in which my observations were 
made I could not be sure that the KneifRa was really indigenous 
where I found it, but like most of our other eastern Onagraceae 
it is distinctly a sun-loving plant (in Georgia preferring dry pine- 
barrens), and possibly if its seeds escaped in dry weather they 
would be injured by the sun’s heat before they could germinate. 
KneifRa was for 4 long time united with Oenothera by systema- 
tists, but the behavior of the capsule now furnishes an additional 
character for separating the two genera. In Oenothera, at least 
in the commonest species, O. biennis, the valves of the capsule 
split apart about half their length at maturity, and remain so 
permanently. 
THE DEFENSES OF THE COCK-SPUR THORN: 
ANOTHER INTERPRETATION. 
By Willard N. Clute. 
The time was when I used to think as Dr. Leavitt does, that 
the thorns of the hawthorns are mainly or solely for defense, but 
after looking further into the matter I am not so sure. I notice 
that at the very time when thorns would be most useful these 
objects on the young and tender shoots are likely to be young 
and tender too, and not particularly obnoxious to the cow or 
other grazing animal. Then again, if a thorn tree knows enough 
to set its thorns in just the right position to puncture the cow’s 
tongue to the best advantage, surely it ought to know that no 
cow can nip the leaders on shoots fifteen feet from the ground 
and yet the plant goes on producing thorns just the same. 
If you will go into the nearest pasture set with hawthorn, you 
may have abundant evidence to show that cows do not refrain 
from eating the hawthorns, thorns or no thorns. Quite on the 
contrary, they apparently consider them good forage for every 
* Dr. Clements has given the name of “ tonoboles ” to plants having this 
mode of dissemination. (Bot. Surv. Neb. 7:47. 1904; Research Methods 
in Ecology, 217. 1905.) 
