330 Evolution in the Plant Kingdom. 
“the asexual-plant.” The asexual spores produce the sex-plant 
again, and so the cycle is completed. The idea of protecting the 
sex-organs or their progeny, begun in the fourth group, becomes 
more and more fully developed in the groups above. After the 
covering to the female-cell is established there remains a neck-like 
passage-way. This passage-way becomes more elongated, and 
more or less guarded, until in the highest group it too is com- 
pletely blocked up by loose cellular tissue, which must be pene- 
trated by what is called the “ pollen-tube.” 
To summarize at this point: we have an asexual group as the 
lowest; then a unisexual group; then a bisexual one; bisexuality 
appearing as the goal in the first three groups. In the fourth 
appears the idea of protection, which gradually becomes more and 
more perfected in method, until, without any sensible break in the 
series, we reach completest protection in the seventh group, or 
Phanerogams. Also in the fourth group, after bisexuality had 
been attained, we find alternate generation, and it is in the devel- 
opment of that character that we find the most striking lme of 
advance from the fourth group to the seventh. Keep in mind that 
the same road is also completely graded and bridged by way of 
“protection,” as has been already referred to. Given, then, as our 
starting-point (1) a sex-plant which carries sex-organs and produces 
ə sex-spore; and (2) a resulting asexual plant which produces 
asexual spores; and remembering that the two are but arcs of the 
, same circle and alternately produce each other, what is the next 
complication that indicates advance ? 
= The next step, besides the completer protection already referred 
to, is the completer setting apart of the two phases, so as to make 
them in structure what they are in function, distinct plants. In 
members of the fifth group, mosses for instance, we find this to be 
the case. The ordinary moss-plant, which bears the sex-organs, 15, 
of course, the sex-phase ; and borne upon it, though as organically 
distinct as if it grew upon any other mechanical support, we find 
the structure which develops from the sex-spore, the so-called 
“fruit,” or spore-case. This is the asexual phase, and produces 
within itself asexual spores (the only spores: meant in the ordinary 
description of mosses). These spores, in turn, produce the sex- 
phase, or ordinary moss-plant, and the cycle is complete. There 1$ 
here a distinct setting apart in function, and, as usually follows, ™ 
. 
