39 



bicarbonic acid and chlorine rises above 0.4 to 0.5%, the cane begins to 

 suffer visibly, even though it be not growing in standing water. 



These figures can, of course, not be considered as a standard in all 

 cases, because a number of other factors influence their magnitude to a 

 greater or lesser extent. Thus the proportion of chlorine to bicarbonic 

 acid may in practice vary within wide limits. Then the influence of the 

 sulfates has to be taken into account, as is so well shown in the study of 

 the second series of analyses. Moreover, the soil of the marsh is not 

 uniform throughout, and its texture and other physical properties and 

 its chemical composition may largely affect the relation between the 

 salt content and the growth of the cane. But it would be virtually im- 

 possible to find all these conditions represented in the field in such a 

 way that each factor may be studied by itself to the exclusion of all 

 other factors. We must therefore be content with such indications as are 

 afforded by the data given in this report ; and in order to study all of the 

 points just mentioned, it will be necessary to carry out experiments with 

 all conditions under perfect control so that each factor may be studied 

 separately. Such investigations will necessarily have to be made in 

 tubs. 



For all practical purposes we may conclude that, at least in this 

 marsh, and in such places where the ground water is sufficiently low, to 

 be out of the reach of the cane roots, the sum of bicarbonic acid and of 

 chlorine may safely rise to 0.4$ , but must be lower where that condition 

 is not fulfilled. 



OTHER MARSH AREAS. 



A few samples of soil were collected in other marshes' on the north 

 coast, and it was found that some of them are extremely salty. The anal- 

 yses are compiled in table XV. 



Sample No. 1 is from the Tortuguero, near Manati, and was collected 

 by Mr. Howells. 



Nos. 2 and 3 were taken in the marsh surrounding the Laguna de 

 San Jose. "\ , 



Nos. 4 and 5 are samples from a marsh belonging to the estate 

 controlled by the San Vicente Sugar Company. The general formation of 

 this marsh is the same as that of the Cafio de Tiburones; it consists of 



