The embryology of Rhytidophyllum 
MELVILLE THURSTON Cook 
(WITH PLATE Io) 
The family Gesneriaceae is tropical and sub-tropical in its dis- 
tribution, but is closely related to certain other families which are 
much more widely distributed. The writer accepted an oppor- 
tunity to make a study of the genus Rhytidophyllum, which may 
be considered characteristic of the family, hoping at some future 
time to be able to make a comparative study of some of the more 
northern species of the related families. The first studies were 
made from R. crenulatum DC. and most of the figures were drawn 
from that material. Later, upon securing material of X. somentosum 
Mart., a comparative study was made. These two species show 
very distinct external specific differences, but the morphology of 
the embryo-sac and embryo is practically the same, the ovules 
and internal structures of R. ¢omentosum being slightly smaller 
than in R. crenulatum. On account of various chemical substances 
of these plants, which are not thoroughly understood, the tech- 
nique was rather difficult and the chromic acid mixtures proved 
absolutely useless. The following mixtures were used with 
SUCCESS : 
(a) Saturated aqueous solution picric acid cg SN Re OIE SE CE 100 ¢.c. 
Glacial acetic acids. ..ci6i..cesise icone Ic.c 
(6) Saturated 70 per cent. alc. sol. picric acid 100 c.c. 
Glacial acetic acid : I c.c 
(c) Saturated aqueous solution picric acid.........s.sseserseseersesess ceeseneettnees 7 100 c.c 
Sulphuric acid A 2c¢ 
(d@) Saturated 70 per cent. alc. sol. picric acid 100 c.¢ 
Sulphuric aci 2 £6. 
The first solution was by far the most successful. The ma- 
terial was then treated in the usual manner, imbedded in paraffine, 
sectioned and stained. 
The ovules assume the anatropous form (figures 1, 2) very 
early. The archesporium originates as a single sub-epidermal cell 
( figures ra, 2). In one instance only, of a large number examined, 
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