of Lysigenous Cavity formation. 405 
In Allium Cepa , while the leaf retains in cross-section the 
semilunar form, the parenchymatous network of central cells 
is wholly living. When the leaf however begins to assume 
its inflated form, accompanied by the great growth in size of 
the peripheral cells, the central network is broken by the 
splitting of cell-walls, so that there arise plates of cells pro- 
jecting freely into the schizogenous cavity and attached along 
only one border of the plate. These cells, however, at this 
time contain a good supply of protoplasm and still live for 
a period, but at last collapse, adding thus lysigenously to the 
size of the already existing schizogenous cavity. 
What has been stated for Allium is true in general also for 
a great many other plants, especially for the peduncle of 
Taraxacum Dens-leonis , the stem of Caltha palustris , and the 
upper internodes of Vicia Faba. In all of these, the cells 
where the cavity is forming suffer a considerable separation 
into plates or strands, so that a large part of the cell- surface is 
exposed to the space of the cleft before any cells die. 
But this procedure is not the one found in all plant-organs 
that form lysigenous cavities during primary growth. All but 
the lowermost internodes of the stems of Cucurbita Pepo , 
Dahlia variabilis , Archangelica sativ a, Myrrhis odorata , Meli- 
anthus major , Ricinus communis , and many other plants, pro- 
ceed no farther in the schizogenous formation of the central 
cavity than to produce ordinary intercellular spaces, or at 
most to increase the size of such spaces to very small clefts, 
before the collapse of cells begins. Thus, for instance, though 
during primary growth the schizogenous formation of cavity 
in the pith of Cucurbita Pepo and Melianthus major is at first 
relatively small, the cavity becomes very large by the collapse 
of a few central cells occurring at a relatively earlier period 
than in the first group of plants cited, and by the subsequent 
great extension of the cells lying just outside those that 
collapse. 
Between these two extremes, in the one of which the 
schizogenous process is of large extent, and in the other goes 
at first but little farther than the formation of ordinary inter- 
