- 20 — 



demonstrated. Leaves which had remained in the dark for 

 two weeks had produced long, sparcely branched rhizoids 

 without any signs of buds. They were then placed in the 

 light and after the lapse of ten days abundant protonema 

 branches were produced from the distal portions of the 

 rhizoids , and also an abundance of buds , thus showing that 

 light was necessary for the formation of buds. Luxuriantly 

 growing protonema without any buds were placed in the 

 dark and allowed to remain for two weeks. The specimens 

 were grown upon pieces of flower pots and at the end of 

 the two weeks no buds had been formed, although the proto- 

 nema from its previous exposure to light must have contained 

 a considerable supply of plastic material, which was used in 

 continued growth rather than in the formation of leafy shoots. 

 No structures at all resembling rhizoids were produced and 

 at the end of the experiment the protonema filaments were 

 beginning to die from lack of food material. From these 

 results it will be seen that in the case of B. capiliare a 

 continued exposure to light is necessary for the production 

 of buds. 



In order to determine whether the cells removed from 

 the basal region of the leaf were able to produce protonema 

 as readily as those of the base, a series of cultures was made 

 in which the leaves were cut transversely through the mid- 

 dle, and both basal and apical portions retained in culture. 

 The basal half of the leaf produced protonema from both 

 the proximal and distal ends, but only rarely from the cells 

 occupying the interior. The apical half of the leaf also 

 produced protonema from the cells next the cut base. 

 (Figs. 17, 18, 19.) Another series of cultures was made in 

 which the leaves were cut lengthwise, and these showed 

 protonema production from the base and also from the cut 

 margins. These experiments then show that almost any cell 

 of the leaf may grow out into a protonema, but that in the 

 cells with one side next the margin, the tendency to form 

 protonema is greater than in those cells which are surounded 

 on all four sides by others. 



