OUTLINE OF STRUCTURAL BOTANY 33 
of the anther and the substance without the application of which 
to the pistil the ovules do not become seeds. 
The yellow dust constituting the pollen when viewed by the 
unaided eye appears like other dust with no especial individuality 
of form. But if we place some grains of it under the lenses of a 
moderately magnifying microscope we see at once that each grain 
is a beautiful organized structure, though there are comparative 
grades of beauty in the grains of pollen from different flowers and 
it is interesting to note that the forms of greatest beauty are not 
always from the most attractive flowers. (Fig. 46.) 
Generally rounded but sometimes spindle-shaped or cubical its 
surface may be elegantly facetted, delicately lined, covered with 
small points or smooth and glistening. Usually the grains are 
dry with little inclination to cohere to each other but in exceptional 
cases they are more or less glued together in little masses such as 
are found in the flowers of the milkweed and orchids so that when 
any part of the pollen is removed from its bed the whole mass 
SITs, 
Fic. 46—Some forms of Pollen Grains.—a. Phlox; b. Monarda; c. Marigold; d. 
Lily—all magnified about 500 times. 
clings to the object which removes it. The grains may also be 
comparatively heavy or comparatively light. In some of the pines, 
for example, the pollen grains are supplied with little air vesicles 
which serve as balloons and enable the grains to float at long dis- 
tances in the air. 
When the pollen grain is brought into immediate relation with 
the stigma it begins to grow into an elongated fibril which pene- 
trates the spongy substance of the stigma and finds its way down 
the channeled pistil till it comes in contact with the ovules which 
at once take on a new form of life and develop into perfect seeds. 
Naturally the amount of pollen produced by individual plants 
will depend largely upon the probable waste that must occur in the 
process of transmission to the stigmas of other flowers than the 
one which bears the pollen. Hence we find a greater abundance 
of pollen produced by wind fertilized plants than by those in which 
the process of fertilization is carried on by the aid of insects. In 
