2i8 The Ohio Naturalist. [Vol. XI, No. 2, 



paragraph to the dividing of the lamina, in which he says: "I 

 have been able to detennine the origin and nature of the cleft. 

 A single row of cortical cells immediately below the epideniiis 

 deliquesces or collapses and the epidermis furrows along the de- 

 pression. The dclequescence 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 epidennal cells come to lie against the middle 

 lamella. The latter then breaks down and the two epidennises 

 are contiguous. The split takes place along the base of the 

 furrow and leaves the two halves of the lamina with apparently 

 nonnal unwounded edges. * * * * The epidermis suffers no disinte- 

 gration during the process. * * * * The furrow of the epidennis 

 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 Macrccystis holds that the inceiJtion 

 of the split occurs as a parting of the superficial layers, which is 

 eventually followed by a swelling or gelatinization (ciuellungen) 

 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 (19U3) writing on Macrocystis gives Will's (1S97) account 

 of the splitting process, which account is also confirmed by Skotts- 

 berg (1907). The fissure occurs b\' 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- 

 derniis 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 in\-estigation 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 Dictyoneuron, 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 



