642 BOWMAN— ECOLOGY AND 



water must be the manifestation of some such principle demon- 

 strated by Haas's experiments. 



The Physiology of the Prop Roots. 



A small series of experiments was made at Miami, Fla., on the 

 transpiration through the lenticels of the pneumatophore or prop 

 roots of older RhiaopJiora trees. Some of these trees were growing 

 along the shores of Biscayne Bay and some along the banks of the 

 Miami River. The salt concentration of the bay is not as high as 

 the ocean outside, due to the effect of the streams which empty 

 into it and the river, of course, is approximately fresh water ; how- 

 ever, the tide produces a noticeable effect in the river and for the 

 comparatively short distance up the river that the mangroves ex- 

 tend there is perhaps a commingling of the fresh water of the river 

 and the salt of the tide ; however, the densities of both the bay and 

 the river were measured with the hydrometer and the measurements 

 wall be discussed under the ecology. 



Essentially the same technique was employed in taking these 

 prop root transpiration records as that used for the leaf records 

 made at Tortugas. The leaf clasp naturally could not be used con- 

 veniently for taking records from the roots, which are cylindrical 

 in shape and of varying thicknesses. To overcome the difficulty of 

 adjusting the transpirometer to this cylindrical surface a modified 

 transpirometer was devised by the writer and made for him by a 

 firm of instrument makers. This device consists of two curved 

 glass sides held in a curved metal frame which is constructed with 

 two grooves along the upper and lower edges respectively. Into 

 these grooves the edges of the indicator paper is slipped and held 

 in place inside the curved glass surfaces. The two curved glass 

 sides are held together on one side by a neat but strong spring, which 

 opens the instrument and permits its being clasped about a root 

 when the two discs of hard rubber are pressed together behind the 

 spring. The indicator paper was inserted and dried over the flame 

 and put into the calcium chloride desiccator. When cool the instru- 

 ment was adjusted to the root and the record taken. As no control 

 could be had over the concentration of the substratum and water 

 concentration in which these old trees were growing, the results here 



