23 



I 



V 



leads to the conclusion that these sharp means of defense serve 

 another purpose, perhaps only secondary, besides that of pro- 

 tection. Upon examination for starch, it was found that 

 there was an unusually large per cent, in the thorns. A thorn 

 of a h(?ney locust, for example, when examined in midwinter 

 is found to consist of a horny exterior, within which is a dry, 

 somewhat powdery, snuff-brown mass, containing no starch. 

 Near the base of the thorn at that place where it is sometimes 

 flexible in its attachment to the stem, when growing, for ex- 

 ample, upon the bole of the tree, the central pith is firm 

 throughout, of a greenish color when freshly cut, and packed 

 with starch. In figure 13, at a, is shown a longitudinal sec- 

 tion, through such a thorn. It is also seen by the same figure 

 that the starch diminishes rapidly in amount, passing upward 

 from the thorn, while below it remains of about equal amount 

 until the lower of the series of buds below each spine is 

 passed. 



The position of thorns being near the bud favors the 

 idea of their serving as places for the storage of starch, for 

 when thus laid away for the winter it is close at hand for 

 use when the growing days of spring arrive. The relative 

 amount at the base of the spine, and below at the point bear- 

 ing the buds, is shown In the cross-section b, and not only is 

 there more within the stem at the juncture of the spine, but 

 the base of the latter is more thoroughly gorged than any 

 other part of the tree. At c is a section shown midway of 

 the internode. 



In the hawthorns the structure of the base of the tliorn is 

 somewhat different. Omitting the discussion of the minute 

 structure of the spine it will be sufficient to call attention 

 here to figure 14, in which the starch, the darkened portion, is 

 seen to occupy the pith of the twig, making a V-shaped 

 structure at the base of the spine. In addition to this, there 

 is a somewhat triangular starch-bearing portion above and 

 below the pith of the base of the spine. In some specimens 

 the starch extends for nearly a half-inch into the spine, but 

 as a slender point. 



In the wild crab {Pyrus corormria, L.), the spine is more like 

 an ordinary branch, because usually bearing buds hpon its 



