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4 
1898 ] THE LIFE-HISTORY OF RANUNCULUS 75 
It would appear that in Ranunculus the cells of the peripheral 
region of the tapetum may be variable in origin. Of course the 
tapetal cells on the axial side of the sporogenous tissue cannot in 
any event be derived from the primary wall cells. The tapetum, 
therefore, is essentially a morphological composite, and is signifi- 
cant only in its physiological relation to the sporogenous cells. 
In its peripheral region in Ranunculus it may be derived from the 
primary wall cell, as in the eusporangiate Filicinee; or from 
the primary sporogenous cell, as in the leptosporangiate Filici- 
nee. Inits axial region it may be derived fromthe adjacent tissue, 
or cut off from the sporogenous tissue. In some cases it seemed 
as though the whole of the tapetum were cut off from the 
periphery of the sporogenous tissue (fig. 4), and in other cases 
( fig. 5) its partial derivation at least from primary wall cells 
seemed equally clear. In the case of an archesporium consist- 
ing of a single longitudinal row of cells, as in Cnicus, it was 
observed that all the cells of the tapetum, with the possible 
exception of a single peripheral one, were derived from the adja- 
cent tissue. While there may be uniformity in the origin of the 
‘apetum in some cases, enough was seen of the history of the 
individual archesporial cells to indicate that the cell of the radial 
‘ow contributing to the tapetum might be sister to the con- 
"guous sporogenous cell, or toa cell derived from the primary 
wall cell. In any event, the main fact seems to be that each 
archesporial cell develops a radial row with a varying number of 
cells; that the innermost cell of this row is sporogenous ; that 
the outer ones are sterile ; and that between the two a special 
ae layer is developed (the tapetum) whose constituent 
ne is determined by position rather then by origin. In gen 
belgee a two layers of cells in the wall of the sporangium 
‘teas € endothecium and the tapetum (fig. 6), but the num- 
ot ee oe between one and three in the same wall. The cells 
mostly ‘sire are occasionally binucleate (fs: 4)s but not 
Hepatic o as in many other microsporangia examined, In 
de a. tapetal cells were observed containing from 
irteen nuclei. 
