1878. | Proceedings of Scientific Societies. 69 
larva takes the same food as the first, its skin is almost entirely 
cast from the coarctate larva, while the subsequent changes are 
independent and entirely free of the shell of this last. 
Tue Iowa ACADEMY OF SCIENCE, Sep. 26.—Among the papers 
read were Observations on the structure of the leaves of Sz/phinm _ 
laciniatum, by President Bessey. The paper embodied the result 
of microscopic observations on sections of the leaves of the com- 
pass plant. As all know, the blade of the leaves of this plant is 
always in, or nearly in, the plane of the meridian, and the purpose 
of the investigation was to determine whether this polarity i is cor- 
related with any peculiarity of structure. In ordinary leaves the 
cells making up the green pulp are differently arranged on the 
two sides of the blade, being packed closely together beneath the 
upper surface, forming what is called palisade tissue. If leaves 
be turned so as to expose the under surface to the sun, they 
either twist the leaf stalk and bring the palisade tissue to the light 
or die. Every leaf makes an effort to keep the proper upper sur- 
face, only, exposed The investigation shows that the two sur- 
faces of compass plant leaves are exactly alike as to structure, 
both in the matter of palisade tissue and arrangement of the 
veins. Both sides therefore are equally affected by light, and the 
equal struggle of the two sides to turn toward the sun gives the 
blade a position about parallel to the meridian. 
A second paper by President Bessey was on dimorphism in 
Lithospermum. This paper was illustrated by diagrams, and 
pointed out that while there is complete dimorphism in Lithosper- 
mum canescens, there is only an appearance of dimorphism in 
Lithospermum longiflorum, due entirely to the varying length of 
the corolla tube. In early summer, the last named plant bears 
_ showy flowers, the corollas of which vary in length from one to 
= two inches. The stamens are always about the same distance 
from the mouth of the corolla, while the stigma borne on a style 
that is nearly constant in length, is sometimes above and some- 
times below them. In place of dimorphism there is simply 
extreme and inconstant variation 
Later in the season this plant produces only minute flowers that © 
are not more than a tenth of an inch in length. These: later flow- 
ers are always self-fertilized. 
Professor Todd read a paper on the distribution of forests in 
= South-western Iowa, with considerations regarding the origin of 
_ prairies, The writer presented facts showing that the position of 
_ prairie and forest is not altogether determined by fires, the fineness 
of the soil, nor even the distribution of rain, but rather by the 
_ constancy of moisture in the air and soil. For ‘example i in South- 
