176 W. Neilson Jones. 
The process of fertilization, then, may be compared with the 
building up of a symbiotic dual organism in which the two partners 
are differentiated by the reactions of the protoplasm of which they 
are composed. It is assumed that the two kinds of protoplasm 
are found isolated, or nearly so, in the male and female gametes 1 
from which the dual organism arises. For the sake of convenience 
of reference the respective characteristics of the two kinds of 
protoplasm will be compressed, in the following discussion, into 
the terms “active” and “passive” (cf. the relations between 
parasite and host). 
It is not intended to suggest that “ activity ” and “ passivity ” 
are the only differentiating traits exhibited by the two kinds of 
protoplasm, and when the terms are employed they must be 
understood to imply two groups of characteristics, of which 
“activity” and “passivity,” although usually well marked or easily 
recognisable, are only one pair. 
When fusion occurs at fertilization, an intimate mixture of 
“ active ” and “ passive ” protoplasm results and, in plants, definite 
bodies such as plastids 2 previously contained within male or female 
gametes now find themselves within a single “ cell ” composed of 
the “ mixed ” protoplasm. At certain cell divisions occurring during 
the development of the zygote, it is conceivable that the coarser 
elements in the cell may become segregated while the finer ground- 
substance remains essentially uniform. Baur explains the occur¬ 
rence of the green and white mosaic areas of certain variegated 
plants ( e.g ., Pelargonium) along such lines. 
Similarly, there seems no reason why the segregation of the 
chromosomes, if these can indeed be regarded as definite entities 
(or as composed of definite entities) distributed in the mixed pro¬ 
toplasm, should not occur without necessitating a separation of the 
zygote into its “active” and “ passive” protoplasmic components. 
1 In the higher animals and plants, it has been questioned whether any 
cytoplasm accompanies the male nucleus into the egg-cell at fertilisation. 
V. H. Blackman, however, has shown that this occurs in the case of Pinus, 
while the genetical behaviour of certain variegated races of Pelargonium has 
received explanation on the same supposition (Baur). Even if no cytoplasm 
accompanies the male nucleus, the nucleus itself consists of a comparatively 
homogeneous ground-work in which the chromosomes are distributed. It 
may well be that this general nuclear ground work is responsible for the 
manifestation of “active” or “passive” characteristics exhibited by the 
gametes. Experiments shewing that enucleated fragments of egg-cells 
attract spermatozoids shed little light on this question. 
1 Among the more primitive groups of plants, such as the Algae, the male 
gamete is usually provided with one or more plastids: in the higher plants, 
however, the male gamete is not obviously accompanied by plastids. (See 
previous note). 
