218 



THE AMERICAN NATURALIST [Vol. XLVII 



This fasciated strain of pea (Mummy Pea or Visum 

 sativum umbellatum) would appear to have been a very 

 constant race, at least since 1597, when it was figured in 

 Gerarde's "Herball." 21 



From the results of hybridization and selection, one 

 may draw the conclusion that the fasciated mutant 

 differed from the normal parent strain by only one fac- 

 tor and that it represents a mutation upon the variabil- 

 ity of which selection has no modifying effect. The 

 character itself appears to be due to one underlying 

 cause and its variableness is only the external manifes- 

 tation of the capricious working of that cause. 



After completing a satisfactory study of the gross 

 aspects of this character, a cytological investigation was 

 made, with the hope that here might be found a clue to 

 the cause or causes underlying the appearance of the 

 anomaly. 



Cytology 



Much trouble in fixing material was caused through 

 the presence of resinous substances in the tissues. Flem- 

 ming's medium and strong solutions were finally found 

 to be the most successful, although prolonged bleaching 

 of the sections with H 2 2 was necessary to eliminate the 

 blackening. Care had to be exercised to secure quick 

 penetration, as poor fixation and shrinkage were likely 

 to result after a bath of over 24 hours. The prepara- 

 tions were stained in Heidenhain's iron hematoxylin 

 and counterstained with clove oil saturated with ery- 

 throsin. This combination usually gave the best results 

 — a deep black chromatin stain against a brilliant red 

 background. Preparations were also stained with the 

 safranin-gentianviolet-orange G combination of Flem- 

 ming and restained with iron hematoxylin. This method 

 gave very sharp outlines, not easily obtainable in some 

 phases, when the ordinary hematoxylin method was 

 used. Another combination which was found valuable 

 in cases where the chromosomes were closely crowded 



"Compare with photograph in Darbishire, A. D., "Breeding and Men- 

 delian Discovery," p. 22, Tig. 8, 1911. 



