410 BOTANICAL GAZETTE | JUNE 
sporogenous, tapetal, and wall tissues, the latter comprising two 
to four layers of cells (fig. 3). These groups of cells exhibit 
nothing unusual either in their development or destiny. The 
inner wall cells are the first to break down, contributing their 
substance to the cells within and leaving the tapetum to forma 
sheath which incloses and nourishes the sporogenous cells. 
Before the final disintegration the cells of the tapetum show 
numerous prominent nucleoli, and quite generally become binu- 
cleate. The two nuclei are plano-convex or concavo-convex, 
with their plane or concave surfaces facing each other (fig. 6). 
The spore mother-cells increase in size, separate, and form 
the usual tetrads (fig. ¢). The mature spore has a smooth sur- 
face, is somewhat angular, and has a diameter of about 304. 
The exospore has three points of weakness, which seem to cor- 
respond to the three exterior angles of the tetrad, and which 
afford points of easy rupture to the tube in germination. At the 
time the spores are discharged, a small proportion of them show 
that the division into the tube and generative nuclei has occurred, 
the latter being the smaller and lenticular in form. Each 
contains a single prominent nucleolus (fig. 5). The subsequent 
history of the microspore was not satisfactorily traced. The 
difficulties of following it through the interval of thirteen months 
intervening between pollination and fertilization are multiplied 
by a copious development of nucleated hairs which takes place 
in the loculus during the interval. Three attempts were made at 
artificial germination of the pollen but without success. In 1898 
the pollen of Q. velutina was shed May 17 and 18 in the vicinity 
of Chicago. 
THE OVULE. 
The first indication of an ovule is manifest after the renewal 
of growth following a period of about eleven months of arrested 
ovarian development. Fig. 7 represents a transverse section of 
the ovary on the date of March 7, and shows the condition 
attained during the first year of growth. The three carpels are 
so fused as to form three nearly distinct loculi. These com- 
municate with one another at the base, but in the middle and 
