20 CENTRAL AMERICAN RUBBER TREE. 



DESCRIPTION AND BOTANICAL CHARACTERS. 



General appearance. — Like its relatives, the tig, the breadfruit, and 

 the trumpet tree, Castilla has a characteristic general appearance and 

 habit of growth which render it very easy of recognition. The trunk, 

 with its rather smooth light-gray bark, has no very striking pecul- 

 iarity, but the slender, simple branches, with their large oval leaves 

 pendant in two rows, are similar to those of very few other trees. 

 These features are perhaps most conspicuous in trees two or three 

 years old, such as that shown in Plate VIII, since the leaves are larger 

 and the slender branches are longer than in trees of greater size. 



The temporary branches of Costilla. — The apparent impossibility that 

 a young tree should have longer branches than an old one is realized in 

 Castilla through the curious habit of self-pruning (PI. X). Such a tree 

 as that shown in Plate VIII has, in fact, no true or permanent branches, 

 which generally do not appear before the third or fourth year. The 

 temporay or false branches have a special layer of tissue at the base, 

 which softens and releases them from their sockets, which are soon 

 overgrown by the bark, so that even the scar becomes almost indistin- 

 guishable. The base of a fallen branch is marked with verv fine 

 edges and grooves radiating from the central pith, which is very 

 small at the joint (PI. XI). It is noteworthy from the botanical 

 standpoint that these temporary or deciduous branches arise from the 

 axils of leaves, while a more permanent or true branch appears as an 

 adventitious hud at the side of the base of a temporary branch. On 

 young trees it is very easy to distinguish temporary from permanent 

 I (ranches, from the fact that the latter are directed obliquely upward 

 at an angle of about 45 degrees, while the temporary branch near 

 which it arises is almost or quite horizontal. It has been supposed by 

 some that all the true blanches are permanent — that is, that they are 

 not provided with the soft basal tissue which enables the others to 

 separate so neatly; but the specimen illustrated in Plate XI shows that 

 in one instance, at least, a branch of considerable size, and itself also 

 } »ranched. had been shed in the same manner as the smaller branches. 

 The typical temporary branches seldom, if ever, attain an inch in 

 diameter at the base, but on young trees they may be 10 or 12 feet 

 long, while the leaves of such branches sometimes measure 18 or 20 

 inches in length. These dimensions are generally decreased to less 

 than half after the tree has attained the mature branching form and is 

 not dependent on a single axis for upward growth. 



The leaves and leaf scales. —A detailed technical description of Cas- 

 tilla would be scarcely in place in the present paper, and is rendered 

 unnecessary by the natural size illustrations (Pis. Ill to VII), which 

 are far more effective than any description could be in conveying an 

 impression of the details of the growing tips of the branches, leaves, 

 flowers, and fruits. 



