Harris — Thorns of Gleditschia triacanthos. 217 



trunk and larger branches is very common in G. friacanthos,* 

 The thorns produced from these adventitious buds are as a 

 rule much larger than those produced in the regular manner 

 on a n(»rmally developed twig. Those on the twig are rarely 

 over 8 cm. in length and never, so far as I have observed, pro- 

 duce more than two branches. These branches are usually 

 small, but in some instances may become quite large, reaching 

 in some cases a length of 25 mm., when produced on a thorn 

 80 mm. in length. The thorns produced from adventitious 

 buds are sometimes as much as 40 cm. in length, usually 

 much branched, the branches large and frequently bearing 

 one or two lateral branches of considerable size. 



The thorns are not produced exclusively on the trunks of 

 large trees but also on those of small shoots, sometimes on 

 those less than an inch in diameter. These thorns are as 

 much branched as those borne on the large trunks. They 

 are also similar to them in form, the only difference being 

 that of size. A thorn 32 mm. long from a sapling an inch in 

 diameter bore six branches and a thorn 37 cm. long from a 

 large trunk also bore six. The largest thorns are produced 

 only on trees of considerable size. Small thorns, similar to 

 those found on small saplings, occasionally occur on com- 

 paratively large trunks. 



On the trunks the thorns are sometimes produced singly 

 but as a rule are found grouped together, as many as three or 

 four sometimes originating on a square centimetre, their 

 numerous branches forming a mass of spines extending in all 

 directions. This grouping of the spines is also noticed In 

 young saplings. It sometimes happens that since they are so 

 crowded the lower branches of these thorns are somewhat 

 distorted. A rather extreme example of this is shown in fig. 

 37. 



In G. iriacaniJios all trunks do not produce thorns alike, 

 but many are found which are entirely free of them. I have 

 not made sufficiently extensive observations to decide what 

 conditions, if any may be determined, are responsible for this. 

 Sargent t siiv-''? i" discussing the size attained by G. triacan- 



* Thorns are also produced iu the same way in G. aqnatica and in G. 

 amorphoides. — See Taubert, I. c. 

 t Sargent, I. c. 



