560 LIFE-HISTORIES ’ ’ 
or certain parts of them, to further protect the embryo and pro- 
vide for its surer and wider dispersal. Hence arise protective shells 
(Figs. 23-36) and various aids to dissemination, including wing-like 
or plume-like appendages (Figs. 55, 59, 76, 159, 197, 215, 248, etc.), 
for catching the wind; elastic springs for propelling the seeds to a 
distance (Figs. 164, 165), and succulent parts (Figs. 88-110) which 
being attractive food, lead animals to swallow indigestible seeds 
and transport them often to enormous distances. Thus, it is in 
plants which form seeds within a case that we find the most perfect 
provision for the welfare of offspring; and it is doubtless because 
of this provision that angiosperms are the dominating plants of 
to-day. 
In concluding our survey of vegetable evolution it may hélp us 
to a just perspective if we briefly review the main steps which the 
ancestors of angiosperms appear to have taken in their long upward 
journey. The accompanying diagrams (Fig. 384) will serve to 
recall the chief facts and conclusions already presented regarding 
the phylogeny of these highest plants, and also the ontogeny of 
modern types representing the supposed links in the series. In 
accordance with the “law of recapitulation” (see page 435) we find 
that the younger the stages the more they are alike, and that imma- 
ture stages of the higher types correspond to mature stages of lower 
types, the youngest stage of each being a single cell like the supposed 
ancestor of all. This reproduces simply by fission, a process which 
is retained by all higher forms as growth by cell-division resulting 
in cell-rows, cell-plates, or cell-masses variously differentiated into 
tissues and ultimately, tissue-systems. Vegetative reproduction 
occurs also in these higher forms through the occasional separation 
of cells or cell-groups capable of independent life. Sexual reproduc- 
tion appears with the fusion of two protoplasts to form one which 
afterward increases by division. In the aquatic forms the fusing 
protoplasts soon became motile and this motility is long retained 
in the male by their descendants while adapting themselves to a 
terrestrial life, and disappears finally when this is fully attained. 
The single protoplast resulting from the fusion of two gives a second 
unicellular beginning and thus the life-history of an individual 
becomes divided into a sexual and a non-sexual stage or generation. 
When the female protoplast remains attached to a plant in the 
sexual stage until after fertilization there results an egg-cell which 
becomes a non-sexual embryo if the connection be maintained so 
that the sexual generation may nurse the non-sexual. This new 
beginning, nursed by the more primitive stage, affords, it would 
seem, a good opportunity for the transition from life in water to life 
on land. Then, too, the nursing, when not excessive, both permits 
and encourages the highest development of the non-sexual genera- 
tion. Finally, it nurses the nurse, and thus through ample provision 
for both nurse and nursling produces a seed well cared for in every 
way. This is the greatest achievement of the vegetable kingdom. 
