* 
562 THE AMERICAN NATURALIST. (VoL. XXXIX, 
There are two types of parthenogenesis in plants : (1) thatin 
the thallophytes where there is no sporophytic generation, and 
(2) that in higher forms when the life history is complicated by 
an alternation of generation. We know nothing of the cytologi- 
cal conditions in the first group including such types as Chara 
crinita, Cutlaria, some species of Spirogyra and Zygnema and 
numbers of the lower Chlorophycex and Phzophycez whose 
motile gametes will germinate like zoóspores should they fail to 
conjugate with one another. But since there is no reason to 
suppose that there are reduction phenomena at gametogenesis, 
the unfertilized gamete is fully prepared with respect to the 
number of chromosomes to continue the parent stock. Dictyota 
must be excluded from this list since the parthenogenetic devel- 
opments here are abortive. In the second group parthenogene- 
sis is likely to prove to be the result of a suppression of reduction 
processes during sporogenesis by which a gametophyte genera- 
tion retains the sporophyte number of chromosomes and in 
consequence is prepared to dispense with sexual processes in the 
development of a new sporophyte.  Parthenogenetic develop- 
ment in animals seems to be similar in its essential cytological 
features to parthenogenesis and apogamy in plants. There may 
be a suppression of reduction processes somewhat comparable to 
that discussed above, which takes place, however, at the time of 
gametogenesis, whereby the egg nucleus retains the number of 
chromosomes characteristic of the parent. Or, through a fusion 
with the nucleus of the second polar body the egg nucleus is 
brought back to the normal condition with respect to the num- 
ber of chromosomes of the parent stock. We cannot, however, 
consider in detail the forms of parthenogenesis in animals. They 
have been recently treated by Blackman (:04b) in comparison 
with conditions in plants. 
Apogamous developments which involve wholly or in part 
other elements than gamete cells and nuclei are likely to be 
established in a number of groups of the thallophytes. The 
author has long believed that the cystocarps of some of the 
Rhodophycez develop apogamously, basing his conclusions on 
certain general peculiarities of the group and more particularly 
on a study of Ptilota (Davis, '96). Three species of this genus 
