550 LIFE-HISTORIES 
or increased in size or otherwise modified to provide for the 
welfare of offspring. 
But however well these plants might succeed in utilizing under- 
ground moisture they could never take fullest advantage of the 
opportunities offered for life upon the land so long as they were 
dependent upon surface water to secure fertilization; and every 
fernwort still retains traces of its aquatic ancestry in the male 
gametes which must swim to accomplish their purpose. Thus fern- 
worts like mossworts are truly land-plants only during part of their 
life, although the former have attained a prodigious development 
upon land. 
Pteridophyta agree with Bryophyta in having archegonia, but are 
distinguished among cryptogams by developing true roots, stems, and 
leaves, in which a vascular system vs developed. 
196. Cryptogams and phenogams. The highest develop- 
ment of plant life is associated with the production of seeds, 
which afford the. best possible provision for the welfare of 
offspring. 
There is abundant evidence to show that the earliest seed-plants 
differed but little from certain fernworts that had developed ma- 
crosporangia containing single macrospores. The first step toward 
converting such a macrosporangium into a seed might easily be 
taken if the macrospores remained attached to the plant until the 
archegonia were exposed, while the microspores, set free, were car- 
ried by wind to the attached gametophyte there to germinate and 
effect fertilization. The final step would come, when, after fertiliza- 
tion of an egg-cell thus doubly protected by nurse-plant and spore- 
sac, the nurse-plant itself should be further protected by continued 
growth of the surrounding parts and should be fed by the parent 
while it was in turn feeding the embryo. An embryo thus fed 
through a connection maintained with the parent plant, and pro- 
tected by a sporangium wall which finally becomes detached from 
the parent for dispersal, is a seed; the macrosporangium with its 
inclosed macrospore and female gametophyte is an ovule; the micro- 
sporangia are anthers; and the microspores, pollen grains. When 
such highly differentiated spore-sacs are borne upon leaves we have 
sac-leaves which we call either carpels or stamens. 
Pines and other gymnospermous plants (Figs. 258, 259, 260, 263) 
as we have seen, bear ament-like clusters of stamens or carpels 
each cluster forming what we may regard as a separate flower. A 
Selaginella which had certain cones producing microspores exclu- 
sively would thus be homologous with a staminate flower of Pinus, 
while an exclusively macrosporic cone would correspond to a pis- 
tillate flower. The morphology of the stamens and their parts in 
