STEVENS: DIOECISM IN THE TRAILING ARBUTUS 541 
of which take part in the development of the endosperm, is that 
of Datura laevis reported by Guignard® (p. 166). 
A “ four-chambered ”’ embryo sac, formed, however, somewhat 
differently from those of Datura and Epigaea, is found in Phy- 
sostegia virginiana. In this species Sharp“ (p. 220) has recently 
observed that the division of the primary endosperm nucleus is 
accompanied by the formation of a longitudinal wall running 
through the middle of the embryo sac. The nuclei of the two 
resulting parts of the sac then divide and transverse walls are 
ee FRI 
on 
Ne 
Fic. 4. Longitudinal section of developing ovule of Epigaea repens, showing 
haustoria which function for the nourishment of the endosperm. X1I90. 
formed. Further transverse divisions then give rise to a large- 
celled thin-walled tissue which fills the ‘‘ endosperm lobe.” 
By the time the embryo of Epigaea reaches the quadrant 
stage the endosperm has a very considerable bulk and shows in 
longitudinal section fifty or more cells. At about this stage a 
knobshaped projection appears at either end of the endosperm. 
These outgrowths extend into the tisshes of the integument and ap- 
parently function as haustoria to nourish the developing endosperm. 
At first both haustoria consist of but a single large cell; and 
this is usually the condition of the antipodal haustorium at 
