88 



transformation of the fertile to the foliage leaf appeared in the 

 plainest manner and in different stages. 



The most marked middle or transition stages, referred to 



n 



above as so desirable to produce, were shown in the tip or upper 



half of the leaf becoming green like the real leaf, while the lower 



part of It was supplied with more or less sorl This is easily ^ 



understood if we remember that the point of vegetation or 



growing point of the fern frond remains apical during its entire 



growth, so the tip might change its character, owing to outside 



circumstances of too recent date to affect the growth of the lower 



part Furthermore, the pinnules of the frond instead of rolling ( 



under as in the ordinary fertile leaf, were spread out flat at the 



tip, this tendency diminishing regularly toward the base. The 



amount of chlorophyll in the leaf tip was equal to that of the 



ordinary leaf At the same time a very remarkable change in 



the position of the frond occurred. That portion on which the 



spores had developed retained the usual upright position, while 



the upper part took on the oblique direction of the sterile leaves. 



In one case, where the line between fertile and sterile parts was 



sharply defined, the upper part bent so strongly as to form almost 



a ri^ht ansrle with the lower. The venation of the fertile leaf was 



t>"^ "**fc> 



modified somewhat, making it agree more or less closely with 

 that of the foliage leaf. The author holds the most remarkable 

 result of the experiment to be, that as the ** vergriinung" advances 

 the development of sori is hindered. When a leaf division changes 

 over to the sterile form before the sori begin to be developed, 

 they are never formed ; but when the formation of sori has begun 

 before the leaflet has been subjected to this outward change, then 

 from the apex to the base all the different stages of sorus building 

 can be found. In one extreme case only an indusium was found, 

 indicating that this organ is the first to originate. Other sori 

 had sporangia pretty well developed, but none produced ripened 

 spores. It must be added here that the season proved a very 

 unfavorable one, so that other ferns of the same genus failed to 

 produce ripe spores. 



The interpretation of the results of the experiment is con- 

 firmed or supported by similar developments occurring on plants 

 growing wild and entirely uninjured by artificial treatment. Such 



