220 PRACTICAL COURSE IN BOTANY 
EXPERIMENT 77. To SHOW THE GERMINATION OF POLLEN GRAINS. — 
Put a drop of 5 per cent sugar solution into a watch crystal or a concave 
slide, seal by smearing the edges with vaseline, and cover with a glass 
to keep out the dust. Examine at intervals of five minutes under the 
microscope (a hand lens will show the result with the specimens recom- 
mended, though not so well), and the pollen grains will be observed to send 
out long filaments or tubes into the sirup, as a germinating seedling sends 
its radicle into the soil. 
246. Office of the flower. — The one object of the flower 
is the production of fruit and seed, and all its wonderful 
specializations and variations of form and color tend either 
directly or indirectly to this end. 
247. Pollination and fertilization. — It was stated in 215 
that only in very exceptional cases can seed be developed 
unless some of the pollen reaches the stigma. This act, 
called pollination, is an essential step in seed production, but 
is not sufficient to secure that end unless it leads to the process 
known as fertilization. Successful pollination is a necessary 
preliminary to fertilization, and the one begins where the 
other ends. 
248. The next step toward fertilization. — Examine with a 
lens the pollinated pistil of a mallow, lily, or other large 
flower, and notice the flabby, withered appearance of grains 
that have stood for some time on the stigma, as com- 
pared with those of a newly opened anther. Can you ac- 
count for the difference? Touch the tip of your tongue 
to the stigma, or apply the proper chemical test, and it will 
be seen that the sticky fluid which it exudes, contains sugar. 
Refer to Exp. 77 and say what effect this substance has 
on the pollen. 
249. The pollen tube. — The same thing happens when a 
pollen grain falls on the moist. surface of the stigma. It 
begins to germinate by sending a little tube down into the 
substance of the pistil, and the withered appearance of the 
grains on the stigma results from the nourishment in them 
having been exhausted, just as the endosperm of the seed is 
exhausted when the embryo begins to germinate. Here, how- 
