254 



The names of the three so-called varieties are given from the 

 .colour of the bark of the trees. 'Hule bianco' is described as the 

 only one worth cultivating, giving thick and abundant latex. 



The tree is not shade-loving, being seldom found in forests, and 

 not easily injured by tapping. ' Hule negro' gives a watery latex, 

 and that of ' Hule Colorado' whilst good, is scanty. 



The plants distributed from Kew and now under cultivation in 

 various tropical colonies, would be more correctly termed, accord- 

 ing to the place of their origin, Darien, " Castilloa" or Darien 

 " Caucho" trees. This would distinguish them from the Ule trees 

 of Mexico, British Honduras, and Nicaragua, and indicate their 

 history. (W. I. BiiUetiii, 1901, p. 350.) 



CLIMATE AND SITUATION. 



The study* of Castilloa furnishes evidence that with this tree 

 there is a relation between climate and rubber production, and 

 that this relation is the opposite of that commonly supposed to 

 exist. Practical experiments in Central America soon showed, 

 that Castilloa will not thrive in swamps or where the drainage is 

 deficient though the need of continuous humidity for Castilloa is 

 still insisted upon. 



The total rainfall of a place affords but the slightest intimation 

 of its climate in relation to vegetation. A sudden, heavy shower 

 may wet the soil much less than the same amount of water 

 falling as a steady rain, and in the supply of water to plants the 

 .difference is even greater; the period during which the atmosphere 

 and soil are moist is of importance to them, but not the amount of 

 water which patters off their leaves or falls into the rain-gauge. 

 Humidity even to the point of saturation for six months may be 

 of no avail to plants unable to survive an e<iual period of drought. 



The lowland forests of the west-coast districts of Guatemala 

 and southern Mexico, while composed in the main of the same 

 tropical elements as those of eastern Guatemala, yet showed a 

 striking deficiency of plants requiring continuous humidity. 

 Nevertheless wild Castilloa seems to have existed in the past as in 

 the present in far greater abundance, the wild product having 

 long been an article of export in quantity far more considerable 

 than from the eastern districts. 



Freer flow of milk in drier ivgioiis. — A second contrary fact to the 

 popular supposition that rubber production is confined to continu- 

 ously humid climates was encountered when it was found that, in 

 spite of the greater dryness, the milk flows down from the rubber 

 trees of Soconusco with a freedom unknown in eastern Guatemala 

 where it merely oozes out into the gashes made by the " uleros." 



Decrease of milk with altitude and continuous humidity. — That 

 rubber milk is obtained with greater freedom on the drier western 

 coast shows that continuous humidity is at least not indispensable, 

 but it does not prove that the larger production is due to the drier 

 climate. There may be, and probably are, differences in the trees 



* Extracts from Bull. No, 49, Bureau of Plant luduBtiy, U. S. Department of 

 Agriculture. 



