No. 464.) STUDIES ON PLANT CELL.— VII. 559 
the embryo-sac in the parthenogenetic Antennaria alpina with 
A. dioica whose ovules are normally fertilized. In A. dioica the 
embryo-sac is one of a group of four cells (tetrad) which are 
formed through two successive mitoses (heterotypic and homo- 
typic) showing the characteristic features of sporogenesis. A 
clear stage of synapsis precedes the first mitosis. The type of 
embryo-sac development in this form is then entirely normal. 
Not only are tetrads suppressed in the parthenogenetic Anten- 
naria alpina but there is no trace of the heterotypic and homo- 
typic mitoses in the embryo-sac. The number of chromosomes 
is very large (about fifty) and evidently the same as is found in 
other periods of the life history. There is then no reduction of 
the chromosomes during the formation of the embryo-sac in the 
parthenogenetic species and the egg and other nuclei in this 
structure have consequently the sporophytic number. There is 
no need of fertilization to bring the egg to a condition when with 
respect to chromosomes it is prepared to develop a sporophyte 
embryo. Juel (:04) notes certain peculiarities in the develop- 
ment of the embryo-sac of Taraxacum officinale. Tetrad forma- 
tion is reduced to a single mitosis and this is not heterotypic, 
since there seems to be no reduction of the chromosomes. 
Details are not given. 
Overton (: 04) finds normal reduction phenomena in the pol- 
len mother-cell of Thalictrum purpurascens which establishes the 
number of chromosomes to be 24 for the sporophyte and 12 for 
the gametophyte generations. These mitoses are thoroughly 
typical of sporogenesis being preceded by a synapsis stage. 
The development of the embryo-sac is of two types. In some 
cases a tetrad of four megaspores is formed from a megaspore 
mother-cell. The nucleus of this cell passes through a synapsis 
and the first mitosis is heterotypic showing the reduced number 
of chromosomes. The lower cell of the tetrad becomes the 
embryo-sac. But many embryo-sacs pass through a different 
history. There is no heterotypic mitosis and no reduction of 
the chromosomes which remain 24 in number. Thus in some 
ovules the mitoses of sporogenesis are omitted and true tetrads 
are not formed, with the result that the embryo-sac contains 
nuclei with the sporophyte number of chromosomes (24) in 
