— 29 — 



The protonema originated exclusively from the ventral 

 surface of the leaf, that is the lamellae side, without reference 

 to the position which the leaves occupied in culture. An 

 examination of the leaves showed that the protonema came 

 apparently from between the lamellae, but the exact origin 

 could only be determined by means of cross sections. The 

 sections showed that the protonema originated from the large 

 cells lying just at the base of the lamellae. (Fig. 34) The 

 protonema production did not seem to be confined to any 

 particiliar portion of the leaf. but was quite generally dis- 

 tributed over the leaf cells occupying the position above 

 named. The portion of the lamin a not covered by the 

 lamellae is small, but the cells from that portion of the 

 leaf as well as the cells of the lamellae were not able to 

 grow out into protonema. 



The first production of buds was noted at the end of 

 about seven weeks, and the same as in Atrichum, in as great 

 abundance in darkness as in light. The buds originated 

 either as modifications of lateral protonema branches or in 

 a few cases by the divisions of the end cell of a main 

 protonema axis. The explaination for the production of buds 

 in darkness ; here as in Atrichum, is to be sought presumably 

 in the nature of the leaf, the accessible supply of nutritive 

 material being considerable. 



The complete Separation of the leaf from the stem was 

 necessary to call forth the protonema formation. The expe- 

 riments with the defoliated stems gave the same results as 

 have already been dascribed for Atrichum. Mention may be 

 made here of the cultures of Pogonatum nanum leaves. 

 Cultures of these leaves were kept for two months without 

 any appearance of protonema, although the leaves were 

 apparently vigorous. 



BRÄCHYTHECIUM RVTABULUM. 



The leaves of Brachythecium did not produce protonema 

 with very great readiness, only about one out of every 

 eight giving rise to protonema. The first production of 



