SELECTION WITHIN PURE LINES OF PESTALOZZIA 149 



all immature stages of development. This completely obviates one great 

 difficulty usually found in the study of size characters, that of determining 

 .which individuals are really small, which only immature. This difficulty 

 seems insurmountable in such forms as Paramecium, but in Pestalozzia, 

 as in Difflugia, the nature of the organism allows size characters to be 

 observed without fear of complications from this source. 



A further word of explanation may be desirable with regard to the 

 assumed absence of sexual reproduction in Pestalozzia. As has been stated, 

 it belongs to the group of Fungi Imperfecti. Many of the species in this 

 miscellaneous assemblage have been found to have other stages in their 

 life-history which have enabled them to be classified under other groups. 

 With few exceptions these other stages of Fungi Imperfecti have shown 

 them to be degenerate members of the Ascomycetes. Many Ascomycetes 

 have both the ascus stage, which follows a sexual fusion, and an asexual, 

 conidial stage. It is commonly assumed that the conidial forms, which 

 make up the Fungi Imperfecti, either have, or have had at some time, a 

 stage with a higher spore form. Whether Pestalozzia now has an unknown 

 ascus stage is not so important, as is the probability that if it had a sexual 

 stage at all, it would be indicated by the appearance of a readily recogniz- 

 able ascus stage. No such form has ever been observed in the hundreds 

 of cultures grown in this series of experiments and it is reasonably certain 

 that it never appeared. From the data gained from the study of analogous 

 forms we can safely assume, (1) that the conidia of Pestalozzia are entirely 

 asexual, (2) that if a sexual stage appears it will result in the production 

 of an ascus form and therefore will be easily detected, and (3) that we 

 have no need to fear that obscure nuclear recombinations are complicating 

 the results secured. 



The unique combination of characters possessed by Pestalozzia and 

 discussed above renders the organism an unusually suitable one for use in 

 study of the results of selection within vegetative lines. Because the 

 fungus was so well adapted for this use and because no similar material 

 had ever been used for this purpose the author was led to undertake the 

 investigation here described. Presented in review, the characters which 

 make Pestalozzia specially desirable for such use are: (1) The presence of 

 numerous distinct strains within the species; (2) the ease with which it 

 is grown in culture; (3) the rapidity with which consecutive generations 

 may be produced; (4) the availability of at least two easily measurable 

 independent characters; (5) the rapidity with which spores are produced 

 and the enormous numbers of spores produced, which enable one to secure 

 significant statistical constants for each generation; (6) the dark colora- 



GENETICS 7: Mr 1922 



