DESCRIPTION ‘OF PLATES. 169 
The result of this “conjugation” has already 
been referred to. 
Pollen grains are formed in the anthers of 
plants in “mother cells,’ by segmentation of 
the contained protoplasm (endoplasm) of these 
cells into four masses, which subsequently are 
invested with a double cellular envelope. The 
external envelope is comparatively thick, and in 
many species is covered with peculiar markings 
or with little spines, which make these pollen 
grains very curious and interesting objects for 
microscopical study, aside from the interest which 
attaches to them on account of the part which 
they play in the reproduction of the plant. 
For the benefit of those who have a micro- 
scope at hand, and who have been at a loss for 
interesting objects to examine, a few of the plants 
having especially curious pollen grains may be 
mentioned: pollen of daisy (Bellis perennis); of 
passion-flower (Passiflora cerulea); of musk-plant 
(Minulus moschatus); of Althea rosea; of pump- 
kin (Cucurbita pepo); of Cobea scandens ; of Ipo- 
mea purpurea; of chicory (Cichorium intybus). 
The compound pollen masses of the different spe- 
cies of Acacia are extremely interesting, and are 
characteristic of the genus (see Plate VI. Fig. 2). 
In Cnothera, the grains have a triangular out- 
line, and in the Malvaceee, they are spherical, and 
covered with short spines. 
The curious bi-lobate pollen grains of the pine 
are seen in Plate VII. Fig. 3. In the city of 
New Orleans, after a rainfall in the spring of 
