Harris - - Thorns of Gleditschia triacanthos. 219 



represents a case in which only the two lower buds have de- 

 veloped at all and tig. 36 a case in which only a bud near 

 the end of the thorn has developed. In tig. 31 is shown a 

 case in which the development of practically all the lateral 

 buds seems to have been induced by an injury to the terminal 

 growing point of the central axis. Here we have produced 

 eleven branches from a central axis 80 mm. in length. Of 

 these, seven are longer than, or nearly as long as, the main 

 axis. 



In July I noticed many of the perfectly formed thorns pro- 

 duced from adventitious buds on trees srowino; in the neigh- 

 borhood of Lawrence, Kansas, which bore leaves below the 

 branches. The same was noticed for trees in St. Louis, 

 Missouri, in October. Not all the thorns thus produced were 

 leaf -bearing but many of them were. The per cent., in some 

 eases, might reach as high as 50. Whether or not the pro- 

 duction of these leaf- bearing thorns is more common one vear 



CD *j 



than another I cannot say. 



The leaves produced on the thorns are quite variable. An 

 extensive description is unnecessary since a glance at the 

 tigures conveys a good idea of their form. They are some- 

 times simple, ovate, sometimes once pinnate, of varying 

 length and varying form of pinnae, sometimes bipinnate, or 

 only a part of the leaflets again divided. 



In speaking of leaf anomalies in this species Penzig says: 

 " Sie treten, nach dem was ich beobachtet habe, leichter am 

 Stock-Ausschlag auf, als an normal entwickelten Zweigen, 

 sind daher an den zur Ilecken verschnittenen oder als nied- 

 rige Straucher gehaltenen Exemplaren haufiger, als an den 

 Zweigen natursviichsiger Biiume." 



The production of leaves on thorns seems to be confined to 

 those produced from adventitious buds. I have never, unless 

 it be in one case, found any indication of such among the 

 thorns of normal branches. 



Of course, as mentioned above, some of the buds produced 

 on these thorns do not develop into thorn branches, and it is 

 not at all uncommon to find leaves whose axillary buds have 

 failed to develop, as in figs. 1, 2 and (J. 



It is of interest in this connection to note that in 1858 



