416 West.—On the Structure and Development of 
The earliest stages agree in every respect with those described above 
under Method i, but the later stages follow a somewhat different course. 
The canal-initials, which arise very early, usually divide into 3, 4, or 6 with 
no obvious increase in size, and give rise to irregular groups of very small 
cells with dense cytoplasm and prominent nuclei (Fig. 1). 
The contents of these small cells immediately begin to show signs 
of incipient mucilaginous degeneration. This brings about a decrease 
in the turgidity of the cells, which tend to round themselves off. At the 
same time small irregular areas are produced between adjacent cells. 
Special interest attaches to these areas, which are only slightly larger than 
ordinary intercellular spaces, since they give the staining reactions of 
mucilage. 
It is quite possible, however, that the mucilaginous substance produced 
at this early stage is derived from the pectin of the middle lamella, which is 
probably the first part of the cell-wall to become disorganized. Such 
a condition indicates how typical schizogenous secretory cavities may have 
arisen. However, the latter are not known to occur in any recent group of 
Cryptogams. 
Strictly speaking, therefore, these mucilage-canals have a schizogenous 
origin ; on the other hand, it is certainly incorrect to say that they have 
a schizogenous development , since all subsequent increase in size of the 
cavity (together with the corresponding increase in volume of the mucilage) 
takes place by the rapid collapse of the surrounding cells. 
It often happens that certain of the more peripheral cells of the group 
divide by walls radial to the centre of the canal; these cells usually retain 
their normal appearance for a considerable time after the innermost cells 
have completely lost their individuality. Thus the young mucilage-duct 
appears to possess a distinct epithelial layer (Figs. 2, 3, and 5). 
But these so-called epithelial cells are very irregular in shape and size 
and have only a transitory existence. Moreover, they do not present the 
appearances generally associated with a living secretory epithelium. 
There is no evidence to show that they have a secretory function ; they 
all very soon break down, their disorganized remains helping to increase the 
contents of the duct. At a slightly later stage epithelial cells can no longer 
be detected lining the cavity of the duct, which now abuts directly upon 
the unmodified parenchymatous cells of the ground-tissue (Fig. 4). 
The adult canals are irregularly distributed throughout the parenchyma 
of the petiole, in which they frequently branch and anastomose (Fig. 5). 
Method iii. Hysterogenetic 1 Lysigenous Mucilage-canals. 
A distinct type of mucilage-duct was found in the adult petiole 
of Kaidfussia aescidifolia and in large roots of Angiopteris evecta . 
1 Frank, 1 . c. 
