36o The Ohio Naturalist. [Vol. XV, No. 1, 



five smaller, and four large, long ones, which are rather well 

 individualized. The chromosomes are attached to a bipolar 

 spindle and are said to undergo a transverse splitting or breaking 

 at the loop end in the first division and a longitudinal separation 

 occurs in the second. 



Lawson made a study of the microspores of several plants and 

 arrived at a number of new conclusions in regard to the relation 

 of "Osmosis as a Factor in Mitosis," (5). He said that the 

 nuclear membrane did not break down or disappear during the 

 development of the spindle, but acted as any permeable mem- 

 brane would under varying osmotic conditions. He gave drawings 

 showing that when the amount of nuclear sap became very 

 much reduced, the membrane drew close to each chromosome 

 and finally there were as many osmotic systems as there were 

 chromosomes and each chromosome has its own sphere of "kino- 

 plasm. " He holds that the achromatic spindle is simply an 

 expression of the tension of the cytoplasm and is not an active 

 factor in mitosis. 



In his paper, "The Phase of the Nuclevis known as vSynapsis, " 

 (4), he states that the condition described is not a contraction 

 at all and has nothing to do with the fusion of maternal and 

 paternal chromatin, so was not a critical stage in reduction. 

 In his study of Smilacina he did not find protochromosomes, 

 but the reticulum was found to be made up of a number of linin 

 threads which approximate the diploid number of chromosomes. 

 Since he found no vacuoles in the cytoplasm he concluded that 

 the nuclear cavity itself was acting as a vacuole, since the spcro- 

 cytes were still enlarging and also on account of the turgid appear- 

 ance of the nucleus. By the stretching of the nuclear membrane, 

 the space within was increased causing a great osmotic pressure, 

 which he concluded facilitated growth. This condition is probabl}^ 

 synonymous with that described by many authors as "synaptic 

 contraction," By actual measurements he stated that he was 

 able to determine that there was no contraction whatever. Thus 

 the conclusion reached in the paper was, that "synapsis" is 

 simply a period of growth during which the great amount of 

 nuclear sap causes the nuclear membrane to distend and with- 

 draw from the chromatin material. This was all explained as 

 occurring before reduction division, because all the sporocytcs 

 had merismatic activity which manifests itself in the two divisions 

 immediately following. 



Schaffncr in his paper, "Synapsis and vSynizesis" (14), defines 

 synapsis as the formation of bivalent chromosomes from uni- 

 valent ones by an end to end fusion and a subsequent folding. 

 McClung's term Synizesis was accepted as appropriate for the 

 contractions usually observed in prepared sections showing early 

 stages in reduction. Synizesis was explained as an artifact 

 probably due to plasmolysis. 



