672 wherry: the habitat of the walking fern 



tion reduces to (a), Table 2. If the California specimen is as- 

 sumed to contain only lead, oxygen, and chlorine, the composi- 

 tion would be as shown under (&). Under (c) is given the 

 theoretical percentage for the formula 6PbO.PbCl 2 . 



It would, perhaps, be rash to claim that the evidence at hand 

 establishes the existence of a definite chemical compound with 

 the formula 6PbO.PbCl 2 , but the composition of the lorettoite 

 approaches more nearly to the requirements of this than of any 

 other simple formula. 



Summary. Lorettoite occurs in honey-yellow masses made 

 up of rather coarse fibers or blades. It is probably tetragonal 

 in crystallization and has a very perfect basal cleavage. Its 

 specific gravity is about 7.6, its hardness about 3, and its fusi- 

 bility about 1. Its luster is adamantine and its streak is pure 

 yellow. It is sensibly uniaxial, optically negative, and its indices 

 of refraction are: w Li = 2.40, e Li = 2.37. It dissolves readily in 

 acid and has the approximate composition 6PbO.PbCl 2 . 



SOIL CHEMISTPtY — A chemical study of the habitat of the 

 walking fern, Camptosorus rhizophyllus (L.) Link. 1 Edgar 

 T. Wherry, National Museum. 



A problem that often confronts the field geologist is the 

 determination of the calcareous or non-calcareous nature of a 

 given ledge of rock, and while a bottle of acid can be carried 

 along and actual tests of the rock for carbonates performed, the 

 existence of an easily recognizable index-plant, which might be 

 found growing only on calcareous rocks, would be a great ad- 

 vantage. In order to ascertain the possible value in this con- 

 nection of the plants classed by botanists as calciphilous, the 

 writer decided to make a chemical study of the rocks associated 

 with such a plant. For this purpose the walking fern, Campto- 

 sorus rhizophyllus, was selected, as it is a fairly common and read- 

 ily recognized plant and is stated in all of the well known botani- 

 cal treatises to prefer a calcareous habitat. 



Samples of the rocks and soils on which colonies of the plant 



1 Published by permission of the .Secretary of the Smithsonian Institution. 



