THE MIcROSCcOPE. 361 
There is no difference in the structure of either motor or sen- 
sitive nerves. It is the centrifugal or centripetal course of the 
contraction that results, in the former instance; in motion, in the 
latter in sensation, 
EXPLANATION OF PLATE. 
Lamella of the cornea of the cat, stained with chloride of gold. 
x 1200. 
A A. Broad offshoots interconnecting the protoplasmic 
bodies. 
BB. Basis-substance, pierced by a delicate reticulum. 
B’. Nerve fibre terminating in the basis-substance. 
CC. Large protoplasmic tract, with nuclei at the points of in- 
tersection, 
DD. Nerve fibres partly terminating in the basis-substance, 
partly in the net-work of the protoplasmic bodies. 
NOTES ON POLLEN. 
JOHN M. HOLZINGER, 
INSTRUCTOR IN NATURAL HISTORY IN THE MINNESOTA STATE NORMAL 
SCHOOL. 
URING the past summer I have taken considerable interest 
in observing the pollen of our native plants, occupying 
spare time on these small grains till I have now a more or less’ 
complete record, with drawings, of the pollen of two hundred 
and twenty species of flowering plants. 
I began by examining them in water, but I soon found that 
this medium swells many grains so greatly that they burst 
almost immediately on being immersed. I therefore followed the 
suggestion contained in Goodale’s “ Physiological Botany,” and 
tried sulphuric acid as the medium; and whenever time per- 
mitted I made measurements and drawings of the grains, when 
dry or immersed in water, or in sulphuric acid, taking note 
whenever a pollen acted unkindly in either medium. The fol- 
lowing points, which were new to me, would seem to be of 
general interest, while some of them may aid others who are 
interested in this line of investigation. 
Most pollen grains swell a little in water. Some expand so 
rapidly that they burst before they can be examined and their 
form determined. Of the two hundred and twenty examined I 
