602 MR A. ANSTRUTHER LAWSON ON 



As this growth proceeds the membrane is gradually withdrawn from the chromatin 

 mass within. 



The result of this withdrawal of the nuclear membrane is the formation of a large 

 clear area of nuclear sap containing the mass of chromatin which has been left at 

 one side. 



No evidence whatever was found to show that any contraction of the chromatin had 

 taken place. 



The enlargement of the nuclear cavity and the consequent withdrawal of the 

 membrane away from the chromatin give the appearance of a contraction, but actual 

 measurements failed to show any diminution in the chromatin area. 



Although no contraction takes place during the growth period of the nucleus, certain 

 definite and important changes take place in the nature of the chromatin threads as the 

 spireme becomes differentiated. 



In tracing the series of developmental stages back, there was some evidence that the 

 reticulum was composed of a number of threads and that this number corresponds with 

 the diploid number of chromosomes. 



As the chromatin passes from the reticulum to the spireme condition, there was no 

 stage found that did not show some evidence of the double nature of the threads. The 

 inference drawn from this is that the chromatin threads are double, even in the 

 reticulum stage. 



During the entire growth of the nuclear cavity there is a gradual shortening and 

 thickening of the chromatin threads until they become differentiated into definite 

 chromosomes, but in no case was there any evidence of a blending or fusion of these 

 bodies. 



It was further found that the actual reduction occurs at a time much later than that 

 commonly known as synapsis. 



My interpretation of the phenomenon known as synapsis is simply that it represents 

 a growth period of the nucleus — a condition that is in harmony with the peculiar 

 organisation of spore-mother-cells. It is a period during which the increasing karyo- 

 lvmph exerts a great osmotic pressure from within. This pressure results in the 

 extension of the nuclear cavity towards an intercellular space where there is least 

 resistance from the neighbouring cells. The chromatin mass is left behind, and its 

 characteristic position at one side of the nuclear membrane is a perfectly natural one. 



LITERATURE CITED. 



Allan, C, E., 1904. "Chromosome Reduction in Lilium canadense" Bot. Gaz., xxxvii. p. 464. 



,, 1905. "Nuclear Division in the Pollen-mother-cells of Lilium canadense," Ann. Bui., xix. 



p. 189. 

 ,, 1905. "Das Verhalten der Kernsubstanzen der Synapsis in den Pollenmutterzelleu von 



Lilium canadense" Jahrb. wiss. Bot., xlii. p. 72. 



