430 BOTANICAL GAZETTE [DECEMBER. 
structures in Polysiphonia are not permanent organs of the cell, but 
are formed de novo with each mitosis, to carry on the mechanism of 
nuclear division. 
HARPER (39) has published an important discussion on a “central 
body” discovered by him in Phyllactinia. In this form the central 
body lies within the membrane of the resting nucleus, and is connected 
with chromatic strands so as to give polarity to the nucleus. The 
poles of the spindles are formed by division of the central body. 
HARPER believes in the permanence of this structure, from mitosis 
to mitosis, and in the maintenance of its connection with the chromatin. 
The permanent nature of the central body in Phyllactinia and the 
transient appearance of centrosphere-like structures in Polysiphonia 
seem at present difficult of reconciliation. 
In Nemalion WoLFE (86) reports that centrosomes are present 
without astral rays at metaphase, but their continuity was not estab- 
lished. The centrosphere described by Davis (18) in the tetraspore 
mother cell of Corallina is formed de novo in each mitosis. Their 
transient nature agrees with the somewhat. similar structures of 
Polysiphonia. 
The reduction oj chromosomes——STRASBURGER’S paper (7 I) 
entitled ‘“‘The periodic reduction of the number of chromosomes in 
the life history of the living organisms” was the first presentation of 
the significance of sporogenesis and reduction phenomena in relation 
to alternation of generations in plants. His conclusions were based 
upon the discoveries that nuclei in the sporophyte generations of 
higher plants have double the number of chromosomes found in the 
nuclei of the gametophyte generations, and that the reduction of this 
double number takes place at the period of sporogenesis. This 
theory has been well established so far as groups of plants above the 
thallophytes are concerned, and the period of chromosome reduction 
has been found to be always associated with sporogenesis, and never 
with gametogenesis as in the case of animals. However, among the 
thallophytes our actual knowledge of facts concerning the reduction 
period is meager. 
Suggestions of the presence of reduction phenomena at gameto- 
genesis have been made among. the fungi. in the Peronosporales 
(ROSENBERG 63) and Saprolegniales (TRow 79). ROSENBERG 
