466 Mr Rattray on the Distribution of Marine Algce. 



(3) A comparison of the "various areas referred to above 

 shows that they are by no means all of equal value with 

 respect to number of different species, some having a rich 

 and diverse floor, others being more uniform and poor. 

 Generally, with certain limitations, uniformity increases with 

 depth. 



(4) The general facies of any given area, as of the 

 entire estuary, varies in summer as compared with winter — 

 the disappearance of many species during winter producing 

 marked changes. 



(5) Transition from one bathymetrical area to another 

 takes place gradually, and not by any sudden or sharp lines 

 of demarcation ; species characteristic of one being almost 

 invariably found in other higher and lower belts, and the 

 sam.e is true with respect to changes observed in horizontal 

 extension. 



On Certain Points in the Morphology of Frullania and some 

 other leafy Jungermanniece. By Professor Alexander 

 Dickson, M.D. (Plate XV.) 



(Part of Presidential Address, delivered lOth December 1885.) 



The subject I have chosen for a few special remarks, on 

 this occasion, is one connected with the morphology of 

 certain of the Foliose Jungermanniese or Scale-Mosses. 



In these plants Leitgeb describes the development of the 

 shoot as taking place by the cutting off of successive seg- 

 ments from an apical cell. This apical cell is in the form 

 of an inverted three-sided pyramid, and from this pyramid 

 segments are successively cut off by septa parallel to its 

 sides. Each cell-segment thus cut off becomes divided by 

 a septum parallel to its free surface into two cells, of which 

 the superficial one — which may be called the Initial Leaf- 

 cell — goes to form the leaf, while the deeper one goes to 

 form the corresponding portion of the axis.* Here we 

 seem to have the most complete realisation of the idea of 

 the leafy plant as built up of successive members — phyta 

 or plant-individuals — each consisting of a leaf with a 



* Leitgeb, Untcrsuch, ii. d. Lcbcrmoose, Heft ii. p. 5. 



