1913] YORK—DENDROPHTHORA 103 
are first distinguished by their larger nuclei and more densely 
staining protoplasm, and without cutting off tapetal cells they 
develop directly into what may be called megaspore mother cells 
(fig. 16). 
JOHNSON’s account of Arceuthobium Oxycedri states that the 
primary archesporial cell divides into two cells. The upper one 
becomes the primary tapetal cell, which later divides by an anti- 
clinal wall into two cells, while the lower cell becomes “the mother 
cell of the embryo sac.’’ Treus’s work shows that no tapetal 
cells are formed in Loranthus sphaerocarpus. He found that the 
archesporial cell in Viscum articulatum does divide into two cells, 
the lower one developing directly into an embryo sac. It is not 
possible to determine the character of the upper cell, since it is 
not known where reduction division occurs. 
Preceding division the megaspore mother cell becomes very 
much enlarged (fig. 16). Later the chromatin thread is organized, 
becomes thickened, and forms a loose mass, the synaptic knot. 
Following synapsis, it segments into chromosomes, which later 
become arranged on the spindle. From two counts of the chro- 
mosomes in the dividing megaspore mother cell nuclei of two 
different ovules at this stage of development, it is apparent that 
18-20 chromosomes pass to each pole of the spindle. The same 
number of chromosomes was found in dividing cells of the young 
embryo. Thus it seems that no reduction division takes place; 
hence this division is a normal vegetative division. Since the 
nucleus passes through what is apparently a synapsis before 
dividing, it may be regarded as analogous to a megaspore nucleus 
of the usual type. The two cells resulting from the division of 
the so-called megaspore mother cell in Dendrophthora are separated 
-by a thin wall and lie just beneath the epidermis of the nucellus 
(fig. 24). The one toward the micropylar region of the nucellus 
degenerates, while the one in the chalazal portion gives rise to the 
embryo sac (fig. 25). _ 
In the seed plants in which parthenogenesis is said to occur 
there is a tendency toward a reduction of the number of divisions 
of the so-called megaspore mother cell. Four megaspores are formed 
in Thalictrum and Eualchemilla. Only two occur in Taraxacum 

