451 



NOTES ON YORKSHIRE BRYOPHYTES. 



11. PALLAVICINIA FLOTOWIANA. 



F. CAVERS, B.Sc. F.L.S. 



(ContinueJ from ' The Naturalist ' for November, p. 444.) 



Where forking- of the thallus takes place, each strand becomes 

 broader and then divides into two, which pass into the branch 

 on the corresponding- side ; at this point a cross-section shows 

 four strands lying side by side. 



The actual proof that these strands serve to conduct water 

 was obtained as the result of some simple experiments. Plants 

 were fixed with the posterior end of the midrib dipping- into 

 waterv solutions of eosin and other stains. It was found in 

 every case that the coloured liquid travelled throug-h the strand- 

 cells much more rapidly than through the surrounding cells. 

 As a rule about half an hour sufficed for the staining solution to 

 travel nearly the whole length of the thallus and to become 

 recognisable in sections taken a little behind the apex, whilst 

 the stain diffused gradually through the tissue around and 

 between the strands. A more striking result was obtained in 

 the following way : — A plant was fixed upright with its lower 

 end in a watery solution of potassium ferricyanide, and after 

 a short time (10-20 minutes) rinsed in water and dipped for 

 about the same time in a watery solution of ferrous sulphate. 

 It was then placed in alcohol, when the midrib showed clearly 

 two dark-blue streaks, indicating the position of the precipitate 

 (' Turnbull's blue'). Sections showed that the precipitate had 

 been deposited in the strand-cells, where the two solutions had 

 mingled. When the plant had been dipped in each solution for 

 a longer time, the cells around the strands also contained a good 

 deal of the precipitate. 



The plants from Coatham were cultivated for several months 

 in shallow, glass-covered dishes, kept moist and well-exposed to 

 the light. They remained health) and produced new branches, 

 but it was found that the latter usually showed no trace of 

 conducting-strands, the tissue of the midrib consisting of nearly 

 uniform cells. There was no trace of lignification in the cell- 

 walls, nor of any elongated cells in the position usually occupied 

 bv the strands, and on cutting off these new branches and 

 dipping the cut end in staining solutions, the latter were found 

 to rise slowlv and uniformly through the tissue of the midrib. 

 It is obvious that when the plants are kept in constantly moist 

 surroundings there is no longer any necessity for the differentia- 



1903 December i. 



