THE DEFENCES OF COCK-SPUR THORN. 
24I 
This is a noteworthy fact. Down-growing shoots are not 
common. Most shoots ascend: either their tendency is to grow 
straight up, away from the earth and toward the light, or, in the 
case of the branch-shoots they tend obliquely upward. Not a 
few constitutionally grow out level. But very few shoots, in 
normal plants, turn their apices earthward. None of the shoots 
of Crataegus do so except the thorns; and it is very singular and 
interesting to find that these branches, so highly modified in form 
by reduction of leafage, limitation as to growth in length, harden¬ 
ing of the bark and wood, and sharpening of the apex, also differ 
from all the other branches of the tree in their physiology. 
For their attitude is a physiological rather than structural mat¬ 
ter. Shoots and roots of plants do not ordinarily grow in self- 
determined directions. Gravity, light, moisture, as stimuli, guide 
the axes in their elongation. The root avoids the light, turns 
toward a moist environment, and by a kind of sense of the direc¬ 
tion of gravity, finds its proper general course through the soil. 
The shoot is gifted with a responsiveness to, or sense of, the lines 
of gravity and of light. These thorns turn downward, we may 
be sure, because while still plastic and growing they are moulded 
by the influence of external forces. 
Such an anomaly in stem-growth calls for a biological “ rea¬ 
son.” Our philosophy seems always to demand proper utilities 
for unusual arrangement and deportment in normal plant life. 
What, then, is the usefulness to the tree of the strong downward 
bent of these spurs ? The answer is doubtless to be found in the 
browsing habits of certain foes of Crataegus. The thorns are 
evident defences against those animals which in a wild state 
feed, or formerly fed, upon the leaves,—pricking their noses, lips 
and tongues. But why should down-pointing thorns be better 
than others? 
The Herbivorae whose depredations were of old the “ reason ” 
for the existence of the thorns in Crataegus and allied plants were 
members of the Bovidae and Cervidae—the ox and the deer 
tribes. We may, therefore, perhaps get the information we want 
by applying to the domestic cow. If we watch her as she feeds, 
we at once see how important a part the tongue plays in securing 
