BoT.— Vol. II.] BYXBEE—LAVATERA. 73 



Summary. 



1. The cytoplasm of the young pollen-mother-cell is 

 made up of two constituents — a fibrous network and a 

 granular substance. 



2. The spindle is formed in the following manner: — 



a. The meshes of the network, close to the nuclear 

 wall, pull out in a direction parallel to the wall, 

 forming a felt of fibers about the nucleus. 



b. The granular constituent of the cytoplasm col- 

 lects in a wide, dense zone about the nucleus. 



c. The linin increases in quantity. 



d. The nuclear wall breaks down and the fibers 

 outside begin to grow into the nuclear cavity. 



e. The cytoplasmic and linin fibers form a mass in 

 which the chromosomes lie. 



f. The mass of fibers projects out at a number of 

 points, forming the multipolar spindle. 



g. Two of the cones become more prominent than 

 the others, which they finally absorb, thereby 

 forming the bipolar spindle. 



3. The process in the second division exactly repeats 

 that in the first. 



4. The granular substance, forming the dense zone, is 

 comparable with the deutoplasm of animal eggs. 



5. Finally, the spindle is formed directly from elements 

 — cytoplasmic and linin reticula — present in the cell from 

 the first, and not from any special spindle-forming sub- 

 stance, or by the aid of centrosomes. 



Botanical Laboratory, 



University of California, 

 October, 1899. 



