Sexual Nuclei in Lilium Martagon . 449 
possible to follow three or four nuclear divisions in such detail 
as to place their true nature beyond a doubt. In the follow- 
ing pages I have tried to do this for the three critical divisions 
of the oogenesis : later on I hope to publish a corresponding 
set of observations on the four spermatogenetic divisions. 
Biological. 
The whole process of the formation of the sexual nuclei in 
Lilium Martagon occupies five or six weeks in May and 
June. At the beginning of this period, transverse sections 
through a number of buds from a single stalk show that the 
embryo-sac is differentiated in each of the median ovules of 
the ovary 1 about the same time that the pollen mother-cells 
are formed in the anthers of the same flower. The process 
of oogenesis is finished when the ovum is formed in the 
embryo-sac, and this takes place as the flower opens. Perhaps 
a day later the male generative nucleus is formed in the tube 
of a pollen-grain from the same flower, so that the two 
processes begin and end together. Nuclear divisions in the 
pollen mother-cell and embryo-sac of the same flower do not 
seem to occur at the same time. On the contrary, an 
alternation of activity is to be observed (vid. Table 1 ). 
The first karyokinesis on either side is preceded by a period 
of growth and development which may be described under 
two heads. 
1. Nucleus in resting condition : it increases in size without 
material alteration in structure. 
2. Process of formation of spirem thread within nucleus, 
including the stage called synapsis. 
1 The upper and lower ovules in each ovary are always smaller than those in 
the middle, and usually in an earlier stage of development. The stage of the 
median ovules is throughout considered typical of that of the ovary. 
