IOWA ACADEMY OF SCIENCES. 
85 
lapse of a week if kept in a moist chamber, he concludes 
that there is not much danger from pollen not germinating 
and fertilizing during cold wet seasons. The anthers of 
the plum will not burst during moist weather, but only in 
dry. 
Leaving these problems, let us retrace our steps, and 
take up a study of the development of the pistil and its 
contents. At the beginning of winter the pistil is well 
formed, the ovary with its single cell and two ovules being 
evident. At this time it is about .45 mm. in length, the 
cells of the ovary is .21 mm. by .14 mm. When growth 
commences in the spring the pistil increases rapidly in 
size, the style becomes much elongated, and the bifid stigma 
appears. At the time of blooming the normal pistil is 
about 4.2 mm. long, the style 8.2 mm. by .14 mm., the 
ovary oval, and about .86 mm. by .27 mm. Structurally at 
this time the pistil is as follows: The stigma consists 
of two sticky lobes closely covered by glandular papillae. 
This forms an ideal receptacle for the pollen as it is carried 
there by the bee. Below these papillae there is a loose 
cellular tissue, and below this the tissue of the style made 
up of an outer cylinder of narrow cells and an inner vascu- 
lar layer surrounding a central cylinder. These cells are 
smaller than those of the interior. The ovary is covered 
by an epidermis the cells of which are rectangular in cross 
section. The cells are for the most part small and irregu- 
lar. After pollination the style withers and falls away. 
The walls of the ovary become thick fleshy, and the fruit 
ripens as a drupe from 2 to 4 cm. in length. 
Late in the summer of the preceding year the two ovules 
made their appearance as swellings on one side of the wall 
of the ovary. By December they are distinctly recogniz- 
able, the ovule having attained a length of 70 microns. At 
this time the archesporium can not be made out with cer- 
t ainty. During the winter the ovule remains practically un- 
changed. Beginning with the latter part of April develop- 
ment is quite rapid. At this time it increases rapidly in size, 
and becomes twisted so as to become distinctly amphitrop- 
ous. The two ovules seem to be identical as to size and shape, 
