l8 BOTANICAL GAZETTE [jaxuary 



threadlike strands in the resting nucleus being only a part of the chro- 

 matin substance that has assumed such a structure. 



Reduction of chiiomosomes axd SYNAPSis.^Since tetrads were 

 first figured by Hexkixg (28) in the maturation division of an insect, 

 several authors have reported the tetrad formation in various animals 

 in connection with the reduction of chromosomes. From studies of 

 the plant cell, the presence of the tetrads in the spore mother cell was 

 independently described by Osterhout (35) and Calkins (ii). 

 OsTERHOUT figured the tetrads in the prophase of sporogenesis in 

 Equisetum. Calkins found in Pteris and Adiantum that the tetrads 

 arise from rings or double rods, parallel or crossed, which resulted 

 from the longitudinal splitting of primary chromatin rods or segments 

 and which break up into four parts (the tetrads), followed by a trans- 

 verse division. An essentially similar mode of tetrad formation was 

 described by Belajeff (5) in Iris and by Atkinson ^4) in Arisaema 

 and Trillium. 



As already described, there is no tetrad formation in Nephro- 

 dium, chiefly due to the fact that both first and second divisions do 

 not occur in rapid succession, and that the appearance of the fission 

 providing for the second division is delayed until after the separa- 

 tion of the bivalent rhrnmn<;nmp<; nf fhf^ fircf 



bivalent chromosomes of the first mitosis. At present 

 most investigators believe that tetrads, in a strict sense, are not 



formed in the majority of cases, excepting in a few groups of 

 animals. 



The nature of these two successive divisions of chromosomes in 

 the spore mother cell has been discussed by many authors, chief 

 attention beinff oaid to nhncipc: nftr^r tV,,. cor,T>-...r,fof,v,„ ^e <^t,„ ^T^.v^m 



o 



into a certain number of chromosomes. Amon^ 

 has been even^ possible variation of opinion. "mIss Sargant (39) 

 found in Lilium that both divisions were longitudinal. This view 

 was soon concurred in by Strasburger (47). Farmer and Moore 



(17) 



and 



(33) concluded that the fission of the chromosomes ia the second 

 division was transverse, and essentially similar results were obtained 

 bylsHiKAWA (30) in Allium, and by Belajeff (5) in Ms. DixoN 



and ScHAFrxER ,^.^ 



btlie 



the continuous thick spirem twists up into loops that are the incep 



