ESTIMATES OF YIELD. 75 



a motive for reporting yields as smaller than they actually were the 

 average reliability of small yields must be taken to be greater than 

 that of large ones, though not, of course, establishing the falsity of 

 higher figures. To the writer, at least, it appears significant that not 

 one of the reported large }delds from planted trees of Castilla has been 

 supported by the testimony of a disinterested witness of scientific 

 standing or even of wide reputation in other lines. Moreover, it 

 seems necessary to attach much importance to the fact that among 

 many planters and other residents of Guatemala and southern Mexico, 

 all more or less directly interested in the possibilities of rubber culture, 

 none was found who had witnessed or who credited the higher figures, 

 but many denounced them as misrepresentations injurious to the legit- 

 imate development of rubber culture. 



An exceptional yield is still an exceptional yield, and not an average 

 which can be used as the basis of general calculation of the profits of 

 rubber culture. To be brief and explicit on this point it may be said 

 that at the present stage of this inquiry 2 pounds per tree is looked 

 upon as the reasonable maximum yield to be expected from adult trees 

 of twelve }^ears and upward, growing under favorable natural condi- 

 tions. This is the highest estimate which is known to the writer as 

 having been made by reliable planters of intelligence and experience; 

 and some such hold that the probabilities lie nearer to half a pound 

 than to 2 pounds. It is appreciated that this estimate is much 

 smaller than many claims based on wild trees, and that it is much 

 larger than the results reached on some of the earlier plantations 

 would seem to promise. The estimate is not, however, made as an 

 average of all published figures, but is reached rather by the elimina- 

 tion of unwarranted expectations from one end of the series, and from 

 the other of disappointments due to adverse local conditions. 



The writer's only opportunity of witnessing the extraction of rub- 

 ber except by small knife cuts was at La Zacualpa, where two of the 

 14-year old planted trees were tapped for his benefit (Pis. XVI and 

 XVII). This was about the first of May, at the end of the long dry 

 season, an unfavorable time for such an experiment. The result 

 was slightly over a pound of rubber, coagulated, and dried on Cala- 

 thaea leaves as previously described; but no reasons were apparent 

 for doubting the claim of the management that 2 pounds of rubber 

 had been secured at one time from neighboring trees of similar size 

 and equal age, The trees tapped were about a foot in diameter at 3 

 feet from the ground, and as shown by the plates, the}^ had been tapped 

 severely and repeatedly. On the same occasion an ulero brought in 

 about 10 pounds of milk, from which 6 pounds of fresh rubber was 

 obtained by coagulation with the juice of Ipomcea; the same pad of 

 rubber weighs about half as much after a year's drying. 



Koschny, whose paper on the culture of Castilla has been accepted 



