Apkil 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 353 



The sections were examined with a one-twelfth Homo- 

 gen. Immers. Zeiss, for the loan of which I have to 

 thank Dr H. Stiles, and with Professor Eutherford's one- 

 eighteenth Homogen. Immers. Zeiss. I take this opportu- 

 nity to express my sincerest thanks to Professor liutherford 

 for the great kindness and courtesy shown me whilst working 

 in his laboratory, and also to thank his assistant Dr Carlier for 

 his constant willingness to help me in my difficult investiga- 

 tion, a help the more valuable to me for the great experience 

 and capability of the latter as a microscopist. All my 

 drawings were sketched with the help of a Zeiss' camera 

 lucida, and not only the outlines of cells, but the minutest 

 details were traced in this way. 



After this long, but not unnecessary introduction, I shall 

 give a description of the development of the embryo-sac 

 based on my illustrations. Plates Ilia and IV. 



When a flower of Myosiirus is fully expanded the 

 gyneeceum consists of an elongated axis bearing at its base 

 a number of mature achenes, at its apex a number in earlier 

 stages of development. This condition enables one, as Stras- 

 burger points out, to get in one longitudinal section most 

 of the essential stages illustrative of the ordinary develop- 

 ment of an ovule, still I did not rely for the study of the 

 earlier stages on sections made through expanded flowers 

 alone, but preferred to select for examination of each of the 

 earlier phases such flowers as showed most ovules in the 

 required stage, for I soon found if two ovules be selected at 

 the same stage of development, but one be taken from the 

 apex of a matured flower while the other be taken from the 

 base of a young flower, that in the latter each individual 

 cell attains a larger size. 



The life-history of the ovule up to the time of fertilisation 

 may conveniently be divided into three stages :• — - 



1. An early stage including the formation of the 



embryo-sac-cell, 



2. An intermediate period ending with the formation 



of eight nuclei within the embryo-sac. 



3. A final stage, during which the ovum matures and 



the primary endosperm-cell is formed by a conjuga- 

 tion of two sexual primordial cells. 



