CHAPTER IV.—INTRODUCTION. 123 
archicarp into a spore, sporocarp, or sporophyte is not possible without a sexual 
act of conjugation, and hereby, to speak generally and without regard to indi- 
vidual details, a morphological ‘complication is introduced. The simplest case 
of the kind, that of the most typical conjugation, may be described as the union of 
two similar archicarps. In other cases male sexual organs are formed differing from. 
the archicarps. The production of these organs is an essential distinction; they are 
essential segments of the stage of the development in which the archicarp 
is formed, and are absent from the other stage which is developed from the 
archicarp. The two stages have therefore been naturally distinguished as 
the sexual and the asexual; the distinction is quite correct since it corresponds 
to that which is the almost universal rule, but it is to be observed that the 
sexual function of the segment in question is of no moment in morphological 
consideration and comparison; and the distinction by putting forward the sexual 
function lays stress on that which is not generally essential, because, as we learn from 
cases of parthenogenesis or apogamy, sexual processes may entirely fail, the 
segments which have usually sexual functions being functionless or altogether 
wanting, without causing any essential change in.the entire course of development. 
It is indeed true that cases of parthenogenesis and apogamy do occur in which 
the elimination of the sexual functions is accompanied by a change in the course of 
the development; speaking figuratively, by a partial flaw or displacement in the curve 
which represents it. This is not always the case, as for example in Chara crinita. 
Instances of it occur in the apogamous Ferns, when the sporophyte, instead of being 
developed out of the archicarp, shoots out from the prothallium beside it or without 
its formation at all. It appears still more strikingly in the formation of adventitious 
embryos observed by Strasburger in certain Phanerogams. Here the course of 
development shows a distinct interruption of the strict homology with the nearest 
allied species, though the homology is at once and completely restored as the de- 
velopment proceeds. In such cases therefore we may speak of zwterrupted and restored 
homologies. 
A further complication of the course of development is introduced by the assign- 
ment of the sexual functions and the corresponding morphological differences to 
different individuals, each the product of a single spore ; by this means the differences 
are carried in extreme cases as far back as to the parent-spore, or, as in the Phanero- 
gams, to the sporogenous segments of the sporophyte. This brief notice of the above 
well-known phenomena is all that is required in this place. 
In the cases which we have been considering the ripe spore usually separates 
from its connection with the parent-organism and developes under favourable 
conditions into a morphologically and physiologically independent individual, to use 
the customary phrase, or into a bion. The sum-total of the bions produced from one 
parent-organism (and from its sisters) is termed a new or the next youngest generation. 
Solution of continuity and development of the separate segments into a new 
and independent generation may also occur at other places in the course of the 
development than that of spore-formation ; the embryo of the Ferns and Phanerogams 
which is developed out of the archicarp is an instance of the kind. If the solution 
of continuity occurs several times and at dissimilar places in the course of the develop- 
ment, as for example in the Ferns, the course of development is divided into unequal 
