STERILE CELLS OCCASIONALLY FERTILE 99 
has been fully made out, is that of Zmesipteris: the normal synangium 
of this plant has when mature two loculi, divided by a septum some five or 
six layers of cells in thickness. Certain synangia of small size are found 
about the limits of the fertile zones: they appear non-septate, and it has 
been shown that the cells of the septum in such cases develop as fertile 
cells, undergoing the tetrad-division (Fig. 58). Such examples show that 
occasionally a reversion may occur from cells normally sterile to the 
function of spore-production. Putting together the two converse series of 
NN 
LIT] bes 
oe = 
Longitudinal sections of ovules showing multicellular archesporia. A, B=Astilbe 
Japonica. 550. (After Webb.) C=Salix glaucophylla. 600. (After Chamberlain.) 
D=Rosa livida. 224. (After Strasburger.) E=Alchemilla alpina. X275. (After 
Murbeck.) #=Callipeltis cucullarta. (After Lloyd.) G=Qwuercus velutina. 720. 
(After Conrad.) From Coulter and Chamberlain, Morphology of Anugiosperms. 
facts—of sterilisation which is relatively common, and of reversion to the 
fertile state which is comparatively rare—two conclusions may be drawn: 
first, that the facts indicate a preponderance of the former over the latter 
in plants now living: in ‘them sterilisation appears to be a more potent 
factor now than reversion, and it has probably been the same in the past 
also. Secondly, it may be stated generally for Archegoniate and Seed- 
bearing Plants, that spore-production is not always strictly limited to, or 
defined by pre-ordained formative cells or cell-groups. 
Voechting has formulated the proposition that ‘No living vegetative 
cell of the plant-body, which is capable of growth, has a specific and 
