220 Trans. Acad. Sci. of St. Louis. 



M, Baillon exhibited * to the Societe Botanique de France a 

 branched thorn of Gleditschia (species not recorded) bearing 

 flowers at the extremities. Where the thorn was produced is 

 not stated but it not improbably originated in an adventitious 

 bud on the trunk. 



On the trunks of trees in St. Louis and the surrounding 

 regions were noticed thorns which had produced two branches, 

 one immediately or close above the other. Several of these 

 are figured. 



While only mature material has been available for study 

 the explanation of this seems to be as follows. There is pro- 

 duced in the axil of the leaf or the leaf scar on the devel- 

 oping thorn, the meristem of an axillary shoot, which is carried 

 forward some dist^ince from the axis of the leaf, and one or 

 more supernumerary primordiums are developed below this 

 primary axillary bud, just as in the normal twig. The pro- 

 duction of the second, and lower, of the branches is to be 

 accounted for by the development of a supernumerary bud. 

 In many cases a small bud may be detected between the base 

 of the branch and the leaf scar. In some cases the lower 

 thorn has become abortive while its development is incom- 

 plete. Even where its development appears at first examina- 

 tion to be complete it is often found to be more flattened, or 

 less terete, than the upper branch, and has something of the 

 appearance of a blighted or withered structure. As may be 

 seen from the figures they show no regularity as to size, 

 being sometimes larger and sometimes smaller than the one 

 above. In four cases, figs. 11, 14, 15 and 22, the lower 

 branches were found producing secondary branches. In one 

 of these cases, fig. 22, the branch of the second order was pro- 

 duced on the lower side of the branch, that is to say pointing 

 towards the trunk. This is the only case I have noticed of 

 a branch of the second order being produced on the lower 

 side of the branch in a plane parallel to the main axis of the 

 thorn. In a few cases these secondary branches have been 

 observed on the upper side of the branches, as shown in 

 fig. 28. When produced here they were sometimes found in 

 addition to the two usual lateral thorns found farther down. 



In these superposed thorns it will be noticed that one 



* Bull. Soc. Bot. France. 5: 316, 1858. 



