REPRODUCTION 51 
main dormant for some time, perhaps for several years, but 
when conditions again become favorable the embryo plant 
within begins to grow again, the seed-coats burst, and a new 
plant, similar to that which bore the flower and seed, is 
formed. 
LESSON XXVII 
# Reproduction—pollination and fertilization 
Materials.—F lowers of various kinds showing adapta- 
tion in form to the problems of pollination. Those of pines, 
willows, walnut, cottonwood, elm, corn, ragweed. 
If favorable regions are available, this and the follow- 
ing exercise should be studied in the field, otherwise abun- 
dance of good material may be studied in the laboratory. 
Suggestions.—That pollination must precede the forma- 
tion of a seed has been seen. It is known, however, that 
pollination of certain kinds produces better plantlets ‘than 
pollination of other kinds. When pollen from the flowers 
of one plant are deposited upon carpels of other plants 
stronger embryos are formed than when the pollen is fur- 
nished by the flower to which the carpel belongs. This is 
called cross-pollination. It is close- or self-pollination if the 
pollen falls upon the stigma of its own flower. Many plants 
practise close-pollination, but it is generally supposed that 
cross-pollination is better. The flowers of many plants 
show most interesting structures for preventing undesirable 
and securing desirable pollination. The two ordinary agents 
of pollination are the wind and insects. 
Observation and study.—Note the general characters of 
the flowers of the corn, pine, etc. Note the abundance of 
pollen, its lightness, and readiness to float in the air. 
Mount and examine some pine pollen and describe any 
special. devices for distribution. Note the soil where corn 
or ragweeds have recently discharged their pollen. To see 
