368 ROYAL SOCIETY OF CANADA 
are formed by the separation of the elements, not by their rupture (Fig. 
1 A). Strasburger, speaking of similar passages, says: “The inter- 
cellular passages may be produced by either of two ways, by the ruptur- 
ing of the cells or by their separation from each other, the schizoginian 
method.” Thus he draws a sharp distinction between the two modes of 
canal formation. 
De Bary, in discussing intercellular passages (3, 213), says: “ Wide 
air-containing chambers and canals, the diameter of which greatly ex- 
ceeds that of the surrounding cells, are produced in two ways. Those 
of the one category arise schizogenetically, and are only distinguished 
from the lacunæ of lamellar parenchyma by their width. The others 
are formed lysigenetically, or better rhexigenetically; during their de- 
velopment a mass of tissue lying in the direction of the subsequent. 

Fig. 1A.—Pteris aquilina, bud of rhizome, tip. Showing purely schizogenous 
canal, C. X 490. 
cavity ceases to follow the surface-growth of that surrounding it, and 
since growth continues in the latter, the former is ruptured and more 
or less destroyed.” 
“To the first, schizogenetic, category belong the air spaces in stem, 
roots, and leaves of many marsh and water plants; Marsiliaceæ, Salvi-- 
niaceæ...., ete. etc.” “~ To the category of lysigenetic forms belong the 
air passages of the Equiseta.... Nelumbium.” 
De Bary confuses some passages of schizogenous origin with lysi-- 
genous formations, for the carinal canals of the Equiseta arise schizo- 
genetically, as in Pteris. However, the boundaries between the two 
formations are often not drawn very clearly, since there may be inter- 
mediate cases, e.g. in the Equiseta the cells which are at first merely 
separated, become broken up sooner or later and lie in the cavity of the 
canal, thus showing lysigenous modification. As will be seen below, this 
is also the case in Pteris aquilina. 

