181 
associated species. They may be abundantly present in one spot, 
but absent in another. These facts make the study of the flora of 
the serpentine barrens especially inviting. According to Dana,* 
serpentine is a hydrous magnesium silicate like talc, but contain- 
ing more water and less silica. It is of a green color, often 
clouded and has been made through the alteration of anhydrous 
magnesian silicates, as chrysolite. It is used asa building ma- 
terial in Philadelphia, the main college hall of the University of 
Pennsylvania being built of it. Because the plant Zalinum tereti- 
Jolium is confined in Eastern Pennsylvania to soil formed by the 
decomposition of serpentine rocks, it is interesting to inquire 
whether the chemical composition of the rocks has anything to 
do with its distribution, especially, as magnesium is so prominent 
an element in the rock’s constitution. The first analysis of the 
plant made from meagre material by Dr. Owen Shinn of the Har- 
rison Chemical Laboratory (Univ. of Pa.) led me to believe that 
such was the.case. Farther analysis with more abundant material 
made by Prof. Henry Trimble, of the Philadelphia College of 
Pharmacy, led to a somewhat different opinion. His letter sub- 
mitting the analysis is here quoted. “The overground portion 
contained so much water that there was not enough material in 
which to more than determine moisture and ash. 
Ash in Abso- 
Moisture lutely Dry 
Substance, 
Overground portion 86.65 % 13.63% 
Underground portion 24.12% 11.15% 
“The ash of the underground portion consisted of potassium — 
sulphate and potassium chloride, also calcium and magnesium 
Phosphate, the magnesium phosphate being very abundant. 
The ash of the overground portion contained the same compounds, 
but apparently in different proportions from what there existed in 
the underground portion, potassium chloride being in this over- 
ground portion in great abundance. How this plant gets so much 
potassium from a magnesian soil is almost a mystery. Certainly 
it is interesting.” It is known that potassium has to do with 
the formation of carbohydrates. If a plant does not find any po- 
tassium in the soil its growth ceases, and the leaves do not oe 
* 1886. Dana, Manual of Mineralogy and Petrology (1894) 33°. 
