222 Trmis. Acad. Sci. of St. Louis. 



least in them occurs most frequently. The thorns produced 

 on one trunk may be well supplied with leaves while those 

 on another may have none. The superposed thorns may 

 occur abundantly on some trees and not at all on others. 



The same observation was made by Penzig, who says in 

 speaking of leaves : ** Sehr oft ist die Tendenz, Blattmonstrosi- 

 taten hervorzubringen, an einzelne Individuen ganz besonders 

 ausgebildet, und man kann an solchen Exemplaren Anomalien 

 der verschiedensten Art vereint finden." 



EXPLANATION OF ILLUSTRATIONS. 

 Plates XXI-XXV. 



Plate XXI. — 1-7. Various forms of leaf-bearing thorns produced from 

 adventitious buds. — 1-6, X^^* ~7, X d* 



Plate XXII. — 8-9. Branches of adventitious thorns, from above, showing 

 size of secondary branches, X ^- — 10-17. Forms of superposed thorns. — 

 I0,X2.-11-17,X1. 



Plate XXIII. — 18-24. Various forms of superposed thorns from adventi- 

 tious buds. — 21 shows a deflection from its course of the main axis by the 

 strong development of lateral branches. The same thing is also to be seen 

 in figure 27.— 18-23, X 1- —24, about X h- 



Plate XXIV. — 25. One of six lateral branches froma thorn 29 cm. long 

 from the trunk of a large tree, from above, showing the production of a 

 lateral secondary branch nearer the end than is usually seen, X !• The tip 

 of the central axis had been broken off, a fact which may account for the 

 very larg'^; size of two of the branches. — 26, A much flattened thorn from an 

 adventitious twig four years old. — 27, Terminal portion of adventitious 

 thorn, showing almost equal size of terminal portion of central axis and 

 the last branch, also variation in the size of the branches, X ^ • — 28, Node 

 of twig from adventitious bud on trunk of large tree. The twig has all the 

 appearance of a large but perfectly -formed thorn except that one of the 

 supernumerary buds has developed into a twig bearing in turn two large 

 branches in the form of thorns (see 29), X h- — 29, A continuation of the twig 

 from fig. 28, X i- — 30, Node of adventitious twig sliowing thorn developed 

 from supernumerary bud, X 1- 



PI. XXV. — 31. Adventitious thorn in which the development of a large 

 number of lateral buds seems to have been brought about by an injury to the 

 tip of the »nain axis,X h— 32, Branch from large adventitious thorn. Not 

 as large as is sometimes found but the largest simple branch noticed, X !• — 

 33, 34, Adventitious thorns which have been injured, apparently by some 

 insect, possibly Cicada, laying eggs in them, X 1- — 35, Adventitious thorn 

 producing branches only near the base, X 3- — 36, Adventitious thorn in 

 which only one of the buds near the end has developed. An uncommon oc- 



to crowding, X 1- 



Issued December 24, 1901. 



