58 INTRODUCTION. 
ficial parthenogenesis, brought about by the use of chemicals and other 
stimuli, have thrown some light upon the subject, but in the opinion 
of the author they are, as yet, far from furnishing an adequate solution 
of the problem. 
In Marsilia vestita Nathansohn (1900) found that it was possible 
to stimulate the egg-cell to a parthenogenetic development by exposing 
the germinating macrospores to a temperature of 35° C. for 24 hours, 
and allowing them to continue their development at a temperature of 
247°C, Asa result about 7 per cent. of the spores gave rise to par- 
thenogenetic embryos. So far as we know, this is the only case among 
plants above the Thallophyta in which parthenogenesis has been 
brought about artificially, and it may be that Aarsz/éa lends itself to 
this sort of experiment more readily because of the fact that in certain 
species the tendency toward normal parthenogenesis is strongly mani- 
fested. In Marstlia drummondiz Shaw (’97) found normal parthe- 
nogenesis to be of frequent occurrence. .In these cases of Marsdléa 
the morphological side of the question, especially the behavior of the 
nucleus, is not known, nor have the number of chromosomes been 
determined in the cells of the parthenogenetic embryo. 
On the animal side of the question the experimenter finds, fortu- 
nately, an abundance of most favorable material in the eggs of sea- 
urchins and of certain marine worms. ‘The results of several investi- 
gators (Wilson, Morgan, Loeb, and others) have shown that the eggs 
of Arbacia and Toxopenustes may be made to develop parthenoge- 
netically through certain earlier stages by subjecting them for a certain 
time to a solution of sea-water, whose osmotic power is increased by 
the addition of a solution of magnesium chloride. The action of the 
Mg-solution seems to be similar to the growth stimulus imparted to 
the egg by a spermatozoén in normal fecundation. 
Equally instructive are the experiments of Winkler (1901) on nucle- 
ated and enucleated fragments of the egg of Cystostra barbata, one 
of the /cacee, which were fecundated by the spermatozoids. Both 
the enucleated fragments and those containing the nuclei developed 
into small embryo plantlets which were exactly alike and attained 
about the same stage of development. 
The development of normally fecundated fragments of egg-cells and 
that of the entire eggs induced to develop parthenogenetically by 
chemical or physical.stimuli are phenomena which seem to fall into 
the same category. They show that in all probability the growth 
stimulus, or the restoration of the power of division and the blending 
of hereditary characters are phenomena which in a measure are inde- 
pendent of each other. Experiments similar to the foregoing have 
