Ig1t] : SHARP—PHYSOSTEGIA 223 
embryo grows rapidly, becomes characteristically dicotyledonous, 
and displaces nearly all of the endosperm. It attains a length of 
nearly 2 mm. in the mature seed, the coat of which is formed from 
the ovary wall. 
Summary 
1. The archesporium of Physostegia consists of a single hypo- 
dermal cell, which, without formation of parietals, functions ; as the 
megaspore mother cell. 
2. The megaspore mother cell by two successive divisions gives 
rise to a row of four megaspores; the chalazal one enlarges and 
gives rise to the embryo sac, while the other three disorganize. 
3. The mature embryo sac contains an egg, two synergids, three 
antipodal cells which multiply to several, and two polar nuclei 
which fuse. 
4. During the formation of the embryo sac a lobe develops 
from near its chalazal end, so that the sac consists of two distinct 
parts joined by a narrower portion. 
5. Double fertilization of the usual type in all probability 
occurs. 
6. The endosperm is cellular from the beginning, the wall 
accompanying the first division of the endosperm nucleus being 
longitudinal through the sac. The chalazal portion of the sac, 
or ‘“‘endosperm lobe,’’ becomes completely filled with endosperm 
tissue, which invades and destroys nearly all of the integument; 
while the micropylar portion of the sac never contains more than a 
very few endosperm cells, and later disorganizes, becoming com- 
pletely obliterated by the encroaching endosperm. 
7. The first division in the fertilized egg is transverse, and the 
chalazal cell, which becomes imbedded in the endosperm through 
the great elongation of the micropylar cell, develops very regu- 
larly into a typically dicotyledonous embryo, which displaces 
nearly all of the endosperm. 
This investigation was carried on under the direction of Pro- 
fessor D. S. JoHNson, to whom the writer is indebted for many 
helpful criticisms. 
