560 THE AMERICAN NATURALIST. [VoL. XXXIX. 
place of the gametophyte (12). The details of the nuclear 
history in these embryo-sacs have not been followed but it is 
plain that their eggs have the requisite number of chromosomes 
to develop sporophyte embryos parthenogenetically. The vary- 
ing proportions of parthenogenetically developed seeds which 
may be found on plants of 7halictrum purpurascens indicate that 
the suppression of normally developed embryo-sacs is not very 
firmly established in this form. 
We now come to a recent paper of Strasburger (: 04c) which 
is the most important contribution to the subject of partheno- 
genesis that has yet appeared. Strasburger studied a number 
of species of Alchemilla from the section Eualchemilla, the 
group which formed the subject of Murbeck's important discov- 
eries. Most of the forms develop pollen in a normal manner 
and Strasburger was able to follow reduction phenomena in this 
process without difficulty. The nucleus of the pollen mother- 
cell passes through a synapsis followed by a heterotypic mitosis 
in which the structure of the chromosomes as bivalent elements 
is apparent. The bivalent chromosomes are in the reduced 
(gametophytic) number. Similarly Strasburger found that some 
species (e. g, Alchemilla pentaphylla, gelida, and grossidens) 
formed embryo-sacs in a normal manner with the presence of a 
tetrad and a characteristic reduction division (heterotypic). But 
the development of the embryo-sac in apogamous species (e. g., 
Alchemilla speciosa, splendens, and fallax) cuts out the two 
mitoses of sporogenesis and no tetrads are formed. The nucleus 
of the megaspore mother-cell emerges from synapsis with the 
sporophyte number of chromosomes and the first division which 
follows is a typical mitosis and not heterotypic. The embryo-sac 
then comes to contain a group of nuclei with the sporophytic 
number of chromosomes in place of the gametophytic and a 
parthenogenetic development of the egg takes place. Stras- 
burger regards the parthenogenetic tendencies of Eualchemilla 
as associated with excessive mutations among these forms through 
which sexual processes are becoming displaced by apogamous 
methods of reproduction. : 
This clear evidence that the cause of parthenogenesis in | 
Antennaria, Thalictrum, and Alchemilla lies in the suppression 
