104 PRACTICAL FORESTRY 
tective scales, and which, on being segregated, is 
capable of producing a plant similar to the single 
parent. Seeds and buds are both reproductive units. 
In addition to the scales which both posséss for the 
prevention of excessive imbibition and evaporation, 
seeds are often supplied with extremely thick, hard 
encasements. 
It appears in the case of the black walnut, for 
instance, that the shell has developed in the course 
of ages as a protection against gnawing animals. 
This is doubtful, because the teeth of the animal 
would grow longer and sharper as the shell of the nut, 
by the process of selection, grows thicker. It is ques- 
tionable whether, by a process of selection on the part 
of the squirrel, the thickest-shelled specimens are left. 
Tt is not possible for the squirrel to determine whether 
the shell is thick or thin, and in fact the walnut and 
hickory seeds which sprout, are usually those which 
the squirrel has accidentally dropped or overlooked. 
The hard shell is probably primarily, at least, for the 
purpose of retaining the proper degree of moisture in 
the fleshy part of the nut, and not to protect it from 
the depredations of gnawing animals. There are 
many who claim that a walnut will not sprout unless 
cracked by frost. It is questionable whether frost 
eracks the shell or not; in fact, walnuts will germi- 
nate in countries where there is no frost, which, of 
