120 Johnson. — On the Development of the 
University, under the stimulating direction of the late Prof. 
J. E. Humphrey, to which any value the work may have 
must be largely attributed. 
The material was collected, partly at New Haven, Conn., 
through the kindness of Prof. W. A. Setchell, and partly 
at Cromwell, Conn. It was fixed in 95°/ 0 alcohol, i°/ o chro- 
mic acid or a 5°/ o sublimate-acetic mixture. For staining, 
gentian-violet or Mayer’s haemalum, the latter either alone 
or in combination with Bismarck brown, were found most 
satisfactory. 
The Development of the Leaf. 
Our knowledge of the development of the leaf in Marsilia 
is due almost entirely to the work of J. Hanstein on the 
embryo, and frequent reference to this will be necessary 
in the following pages. 
The leaves arise in two rows, one on each side of the 
median line on the dorsal surface of the stem. Each leaf 
is developed from a typical two-sided apical cell formed 
from part of one of the dorso-lateral segments of the tetra- 
hedral apical cell of the stem. This apical cell of the leaf is 
recognizable when the stem-segment in which it is formed 
is only the third or fourth in its series from the apical cell 
of the stem. It is larger in size and projects more than 
the neighbouring cells ( L , Fig. i), and its position is such 
that its edges are directed toward the base and the apex 
of the stem. 
Hanstein (’65) has already shown the shape and position 
of the apical cell to be as above described in all but the very 
earliest leaves of the embryo of Marsilia , which agrees thus 
with most other Leptosporangiates that have been studied. 
They have been thus described by Hofmeister (’62) in 
Aspidinm , by Kny (’75) in Ceratopteris , by Klein (’87) in 
Polypodium , by Meunier (’87) and Bower (’89) in Pihdaria , 
by Campbell (’87) in Onoclea , and by Bower ( 89) in Tricho - 
manes. Pteris is apparently the only known case where, 
