SELECTION WITHIN PURE LINES OF PESTALOZZIA 145 



Thus far Protozoa have been used in most of the critical and extensive 

 investigations, and these organisms are not only subject to great environ- 

 mental effects, but give rise to only two offspring at a time, a serious dis- 

 qualification for the most accurate results. JOHANNSEN'S original material, 

 the garden bean, was ideal from the standpoint of number of offspring, 

 but, reproducing sexually, it offered a possibility of Mendelian segregation 

 obscuring the true fluctuation which it was desired to study. The Fungi 

 Imperfecti seemed to afford an ideal material, combining the advantages 

 of numerous progeny with uniparental, non-sexual reproduction. 



REASON FOR THE CHOICE OF PESTALOZZIA 



P estalozzia Guepini Desm., one of the Fungi Imperfecti, was chosen by 

 the writer as a species unusually well suited for use in the study of the 

 selection problem. The species is polymorphic, containing a number of 

 different strains, so that it is not unlikely that new strains are being formed 

 at the present time. It is very easily grown in culture in the laboratory 

 and does not require tedious, special methods. Sporulation occurs readily 

 in culture, and development from the spore to the fruiting stage requires 

 only a few days, so that generations can be grown in rapid succession. 

 Spores are produced in enormous numbers so that more than enough are 

 always available for observation. They possess two characters that are 

 capable of accurate measurement, and a change in color at maturity en- 

 ables one to tell with certainty which spores are mature and which imma- 

 ture. Size characters may therefore be studied without fear that forms 

 apparently small are only immature. In addition to these advantages the 

 spores are produced, as in all Fungi Imperfecti, entirely asexually, so that 

 there is no possibility that the results are influenced by sexual phenomena. 



P estalozzia Guepini Desm. is widely distributed in the eastern tropics, 

 where it causes the gray-blight disease of tea, and leaf-spot diseases of 

 cocoanut, betel nut palm, African oil palm, Para rubber, and doubtless 

 many other wild and cultivated plants of those regions. The species con- 

 tains a number of forms which differ more or less markedly from one anoth- 

 er in morphological characters. Some of them are likewise supposed to 

 be restricted to particular hosts. Strains occurring in regions far removed 

 from areas known to contain Pestalozzia Guepini, and on hosts not previ- 

 ously reported for this fungus, have been described as new species. This 

 is only natural, for the species was originally not closely defined. The 

 new species however, are even less perfectly described than P. Guepini, so 

 that one gains nothing by using their names. For the purposes of this 



GENETICS 7: Mr 1922 



