called arehegonia, enclosing and protecting the egg-cells. When 
fertilized, the egg-cells develop into special structures (sporo- 
gonia ), which produce spores. There is thus a distinct alterna- 
tion of generations. 
3. To grow on the “dry” land it became necessary for the 
plants to take up moisture from the soil. In the clubmosses appear 
absorbing roots, with root hairs, and a vascular system. The 
leaves are small, as in the mosses. The sperm- and egg-producing 
generation (the prothallium) is here comparatively inconspicuous. 
The sperms of clubmosses have two cilia, like the bryophytes ; 
those of horsetails and the higher plants are multiciliate. 
4. The nutrition of green plants requires the action of light. 
The ferns develop large leaves, with greater capacity for food 
making. These leaves have numerous spore-cases on the tinder 
side , while the smaller leaves of clubmosses have a single spore- 
case on the upper side. In the water-ferns (and also in Selaginella) 
there are two sizes of spores. 
5. In the seed-bearing plants there are always two sizes of 
spores. In the ferns and lower plants the spores usually fall to 
the ground and there germinate and are fertilized. In the seed- 
bearing plants, however, the large spore remains in its place on 
the parent plant, germinates and is fertilized by the sperm from 
the small spore, brought to it by wind or insects. This results 
in the production of a seed, which is really a young plantlet (with 
surrounding structures) capable of remaining in a dormant con- 
dition for a considerable time. 
6. The cycads and ginkgo, like the algae, mosses and ferns, 
have swimming sperms, thus needing water for fertilization. In 
the conifers and angiosperms the sperms are not swimming. 
7. The lower seed-bearing plants, or gymnosperms, have 
naked seeds. In the angiosperms, which are the true flowering 
plants, the seeds are enclosed in an ovary, which develops into a 
fruit. 
The angiosperms form two main groups. The dicotyledons 
are nearest to the gymnosperms. They have two seed-leaves, 
leaves netted-veined, and floral parts usually in five’s or four’s. 
Within the dicotyledons, woody forms have usually the most 
primitive characters. The evolution of flowers occurs along many 
lines, from parts (sepals, petals, stamens or carpels) all separate 
to these parts more or less united. Other developments are from 
regular to irregular flowers, that is, toward increasing adaptation 
to insect pollination. In general, herbaceous plants and those 
with united petals have less primitive characters. 
The monocotyledons are a side line with one seed-leaf, leaves 
mostly parallel veined, and floral parts usually in three’s. 
Alfred Gundersen. 
The Leaflets are published weekly or biweekly from April to June, and 
October to November, inclusive, by the Brooklyn Botanic Garden, Brooklyn. N. Y. 
Telephone: 6173 Prospect. Mail address: Brooklyn Botanic Garden. Brooklyn. 
N Y 
