No. 464.) STUDIES ON PLANT CELL.— VII. 567 
ciate the term fertilization with this phenomenon, whatever may 
be the physiological significance of the nuclear fusions, because 
we are not dealing with gametes and there cannot be involved 
in the process anything of the long phylogenetic history of sex- 
ual differentiation in the group. We considered these matters 
in some detail in that portion of this section entitled * Fertiliza- 
tion." 
With respect to the factors which determine apogamy it must 
be confessed that we are still in the dark. Lang’s ('98) studies 
on fern prothalli, however, throw some light on the problem. In 
some twenty forms of the Polypodiaceze apogamy resulted when 
the prothalli were kept from direct contact with the water (7. e., 
were watered from below) and exposed to direct sunlight. 
When watered from above these same forms developed normal 
embryos from eggs. It is clear that the suppression of condi- 
tions which make fertilization possible (7. e., water over the sur- 
face of the prothallus), possibly aided by sunlight which may 
cause irregularities of growth, induced the development of cylin- 
drical processes from which the apogamous sporophytes arose 
and which bore sporangia in two forms. It seems hard to draw 
more precise conclusions from these experiments other than that 
the normal life history is checked at a critical period (fertiliza- 
tion) and the plant is forced into expressions of vegetative 
activity. The conclusions of Farmer, Moore, and Digby (:03) 
offer an explanation of how the developments may take on 
sporophytic characters through the fusion of nuclei in the tis- 
sues and the establishment of a sporophyte number of chromo- 
somes. 
Strasburger suggests that apogamy in Alchemilla may be the 
result of a weakening of sexual power associated with excessive 
mutative tendencies. This would seem to imply that excep- 
tional vegetative activity, with the appearance of much variation 
under favoring conditions, may be combined with apogamy. It 
is of course a well known fact that a high degree of cultivation 
tends to lessen the fertility of a form unless guarded by careful 
selection. A weakened sexual fertility due to excessive vegeta- 
tive activity is likely to be replaced by forms of vegetative 
reproduction. When the process of sporogenesis becomes so 
