1900] THE CELL PLATE IN HIGHER PLANTS 169 
necessary for the formation of a cell wall, there would be some 
evidence for the hypothesis that the nucleus forms the cell wall 
substance. 
The investigations described in the foregoing pages were 
begun at Lake Forest University under the direction of Profes- 
sor R. A. Harper, whose helpful interest and valuable criticism 
have continued throughout their progress. The work was con- 
tinued and practically completed in the botanical laboratory 
of the University of Michigan during the years 1897-8 and 
1898-9. I wish here to thank Professors Spalding and New- 
combe of the above laboratory for the liberal way in which 
material and equipment were provided, and for many helpful 
Suggestions received. Professor Jacob Rheigard, of the depart- 
ment of zodlogy of the University of Michigan, very kindly 
allowed the use of the photographic apparatus of that depart- 
ment, and Dr. J. B. Johnston aided me greatly in making the 
photographs. 
THE UNIvERsITy OF WISCONSIN. 
EXPLANATION OF PLATES VIII AND IX. 
_ Figs. 1-21 are reproductions of photographs made with the Zeiss photo- 
Ps aa apparatus. (Figs. g and 22 have been purposely omitted.) 
ig 23-31 are from drawings made with the aid of the camera lucida, Zeiss 
ae eiageioag objective, and compensation oculars 8, 12, and 18, The size 
€n reduced 4 in reproduction. 
Figs. 1-10. Larix ; pollen mother cells. 
Fig. 1, Equatorial plate. x 750. 
ohne ym diaster showing first stages in preparation for cell plate 
Fig i central spindle is differentiated into three zones. X 1200. 
% wag than preceding ; central spindle alike throughout. X 1200. 
: “tae plate elements just forming. x 1200. : 
a Bsc oung cell plate has begun to grow in area; connecting fibers 
§ to disappear. x 1200. 
F 3 . 
"GS. 6-10. Later stages in the growth of the cell plate ; see explanation 
00, 
Figs. 11 
Fig, 13, 
—21. Allium Cefa,; cellof growing root-tip. 
Equatorial plate; spindle fibers arranged into strands or 
500, 
