10 MB. B. SPBUCE ON THE MODE OF BBANCHING 



of this mode may be naturally looked for in plants with whorled 

 leaves and terminal inflorescence ; and the branches in each fascicle 

 will often be fewer than the leaves in each whorl. In Rauwolfia, 

 an Apocyneous genus which has the leaves 4-5-nate, the ramifica- 

 tion is regularly 3-chotomous, of which JR.polyphylla, Benth., Ran- 

 wolfia PI. Am. 1732, and B. PL Am. 3856 are examples. But 

 there are numerous cases of isochotomous ramification in trees 

 with alternate leaves, as, for instance, in most species of Croton, — 

 though the trees of this genus which produce the South American 

 " dragon's-blood " show a combination of verticillate and isochoto- 

 mous branching, the trunk or primary axis being continuous or 

 excurrent, and the secondary axes deliquescent : so the general 

 outline is still conical, though the branches are fan-shaped (for 

 they are isochotomously divided in the same horizontal plane). A 

 good example of this is a beautiful Croton (PI. Am. 4582 — the 

 "Sangre de drago " of Maynas) gathered at Tarapoto. This is a 

 straight tree of 80 feet, with nearly black shining bark ; the first 

 branches are from three to six in each whorl (three stouter, and 

 one to three slender supplementary branches alternating with the 

 former and often inserted a few inches below them), and they are 

 3-6-chotomously divided. Several other Euphorbiacea resemble 

 the Orotons in their isochotomous mode of branching. Manihot 

 Aypi (the " Yuca dulce " of Maynas, whose nutritious and harm- 

 less root supplies the inhabitants with a moiety of their food, 

 as the poisonous root of M. utilissima does the inhabitants of 

 Brazil) has the stem four times trifid, the branches forming with 

 each other nearly a right angle (80°-88°). In a wild species of 

 Manihot from Tarapoto (PI. Am. 4287) there is the same tricho- 

 tomous ramification, and the long weak branches thread, almost 

 twine, among the adjacent bushes. 



Some Ericece, especially certain species of OaultJieria frequent 

 in the Quitenian Andes, have a fasciculato-3-5-nate (nearly isocho- 

 tomous) ramification. 



The ramification of some species of Theobroma is partly verticil- 

 late and partly isochotomous. Tk. subincanum, Mart. (PI. Am. 



together than the primary. This is analogous to what occurs in verticillate ra- 

 mification, where the secondary or tertiary branches are frequently alternate. A 

 little observation shows us that, as we proceed from the primary axis to the apices 

 of the remote axes, there is a tendency to a straightening out of the spirat, in 

 the insertion of both leaves and branches. This is well seen in several Hypna, 

 where the leaves, 8-stichous on the stem, become 4-stichous or even distichous 

 at the apices of slender elongated shoots. 



