492 
F. L. PICKETT 
December 17. Branches have grown from tips and sides, and 
rarely from apical cells, in every way like the attenuated growths 
referred to above (figs. 15, 16, 17, 18, 29, 32, 33). 
December 29. The extensions have grown up to a maximum of 
three cells in length (figs. 25, 26). Culture returned to strong light, 0.8. 
January 5. Plants show normal beginnings of plates at the tips 
of second attenuations (figs. 13, 14, 19, 21, 22). 
This culture was allowed to remain in full light. Each plate 
formed at the tip of an attenuated cell grew normally as an independent 
Fig. 19. Prothallium of A. platyneuron showing outgrowths from dififerent 
parts to form independent plants, as a result of a period of reduced light followed 
by a period of stronger light. (X 52.) Traced from a photomicrograph. 
plant. The primary plates also continued normal growth. In each 
citation given above the figures are from plants taken from one culture 
at one time, and usually from a single mass removed on a needle point. 
The above account is that of a typical culture. There were 
variations in time and extent of reaction, due to weather conditions; 
but there was always a marked reaction in some plants and a seeming 
indifference in others. This individual difference is a point of special 
interest, manifested at every change in condition, and will be discussed 
at length. 
Every culture subjected to variations of light intensity sufiicient 
to produce changes in the manner of growth, has presented upon 
examination two groups of plants. The greater number of plants 
show reactions as described above. Some plants — about 25 per cent 
of each culture — on the other hand, show no noticeable reaction to 
light changes. In order to make sure that age had nothing to do with 
such variation, cultures were made by sowing spores on distilled water, 
and after three weeks when all viable spores had produced rhizoids, 
