The Ohio Naturalist. 
[Vol.XI, No. 2, 
2 18 
paragraph to the dividing of the lamina, in which he says: “I 
have been able to determine the origin and nature of the cleft. 
A single row of cortical cells immediately below the epidermis 
deliquesces or collapses and the epidermis furrows along the de- 
pression. The delequescence is propagated to adjacent cells, 
right and left, and continues down the middle lamella. The fur- 
rowing may take place along one surface of the leaf or along both 
surfaces until the epidermal cells come to lie against the middle 
lamella. The latter then breaks down and the two epidermises 
are contiguous. The split takes place along the base of the 
furrow and leaves the two halves of the lamina with apparently 
normal unwounded edges. * * * * The epidermis suffers no disinte- 
gration during the process. * * * * The furrow of the epidermis 
seems to deepen destroying the inner cells of the lamina as it 
progresses.” In other accounts the central idea has likewise 
been an association of a process of cell disintegration or gela- 
tinization with the inception and advance of the split. Rosenthal 
(1S90) in his discussion of Macrocystis holds that the inception 
of the split occurs as a parting of the superficial layers, which is 
eventually followed by a swelling or gelatinization (quellungen) 
of the pith-web. In this modified pith-web a cavity is formed, 
which, enlarging, finally meets the gaps already developed in the 
upper layers and the lamina is divided. No discussion of the ori- 
gin of either the inner cavity or superficial clefts was given. 
Reinke (1903) writing on Macrocystis gives Will’s (1897) account 
of the splitting process, which account is also confirmed by Skotts- 
berg (1907). The fissure occurs by the formation of an elongated 
cavity filled with a jelly-like substance, arising through gelatini- 
zation of the inner tissues. The furrow or depression which pre- 
cedes the cleft is formed by a sinking or pushing in of the epi- 
dermis due to increased division of the cells overlying the gela- 
tinized portion. 
Because of the brief and fragmentary nature of the accounts 
heretofore given, it was believed that a fuller investigation of the 
matter would be desirable. Further it was thought important 
to make a comparative study of the splitting processes in the 
different genera available, in three of which, Postelsia, Lessoniop- 
sis and Dietyoneuron, these processes have heretofore never been 
described. Material for the five genera investigated was in the 
collection of Prof. Robert F. Griggs of the Ohio State University, 
to whom I am greatly indebted, not only for material, but for 
much valuable advice and criticism throughout the course of the 
study. In view of the diversity found between the different gen- 
era, it would be very interesting to study Lessonia and Pelago- 
phycus also, but material of these genera could not be obtained. 
A part of the plants studied were killed in chrome-acetic acid 
and part in formalin. The usual methods of microtomy were 
