468 
Notes . 
the Edinburgh and Kew collections. It would appear probable that it 
is a peculiarity which may be induced, or at least its further develop- 
ment promoted, in certain species by particular conditions of culture : 
it is to be remembered, however, that it is not readily induced by 
moist culture in ordinary ferns, as I have shown by experiment 1 , and 
in ferns at large it is certainly of rare occurrence. Since I know of 
no reference to this abnormality in systematic books, it would appear 
to be uncommon or even absent in the specimens of Trichomanes 
from their native habitat, upon which systematic writers will have 
based their descriptions. 
In this, as in other cases of apospory, it is difficult to define the 
exact limit of the parts representing the two generations : examining 
them externally, the form and nature of the appendages (rhizoids, 
or sexual organs) and of the constituent cells have been used as 
diagnostic characters ; it is possible, however, that the constitution of 
the nucleus may come to be recognized as a strict diagnostic character. 
If the generalization be correct, that the nuclei of the gametophyte on 
division show only half the number of chromosomes shown by those 
of the sporophyte, then clearly the cells in which the reduction takes 
place will be those which will define the limit between the generations; 
on this point detailed observations will be awaited with peculiar 
interest. 
F. O. BOWER, Glasgow. 
Oct. 1894. 
ON THE ASCENT OF SAP 2 .— By Henry H. Dixon, B.A., 
Assistant to the Professor of Botany, Trinity College, Dublin, and 
J. Joly, M.A., Sc.D., F.R.S. Strasburgers experiments have elimi- 
nated the direct action of living protoplasm from the problem of the 
ascent of sap, and have left only the tracheal tissue, as an organized 
structure, and the transpiration-activity of the leaf wherein to seek an 
explanation of the phenomenon. The authors investigate the capabi- 
lity of the leaf to transpire against excessive atmospheric pressures. 
In these experiments the leaf was found able to bring forward its 
water meniscuses against the highest pressures attained and freely 
transpire. Whether the draught upon the sap established at the leaf 
during transpiration be regarded as purely capillary or not, these 
1 Annals of Botany, Vol. iv. p. 168. 
2 Abstract of a paper read before the Royal Society, November 15, 1894, 
