1893- NOTES AND COMMENTS. 249 



usually 4, metres, and constituting the Nupharctum. Sometimes it is 

 associated with species of the preceding zone, chiefly Potamogeton 

 natans, while the water milfoil (MyriophylliDii), Potamogeton perfoliatus, 

 and others of the following zone begin to appear. 



3. The third zone, or Potamogetonetum, is formed by plants different 

 according to the lake ; sometimes pondweeds, chiefly Potamogeton 

 perfoliatus, then P. lucens, or P. crispns, less often Myriophyllum spicatum, 

 or still more rarely the mare's-tail [Hippuvis vulgaris), all bearing their 

 leafy and flowering branches at or near the surface, on stems 4 to 6 

 metres long. Their rootstocks occupy the edge of the slope, below the 

 yellow water-lily, at a depth of 4-5 metres, descending to a depth of 

 6 and 7 metres. Here also lives the hornwort, Ceratophyllum demersum, 

 which, after wintering in depths of 3 to 6 or even 8 metres, breaks 

 loose and becomes quite free, floating like the bladder-wort {Utricnlaria 

 vulgaris) . 



4. The fourth or deep zone, the Characetum, is formed by plants 

 which never reach the surface, but remain always fixed to the bottom 

 at a depth of 8, 10, and 12 metres. Such are the numerous Characeae, 

 Naias major, and the mosses Fontinalis antipyretica and Hypuum gigauteum. 



In deep lakes with rocky borders, plant-life is absent or repre- 

 sented only at points where erosion or a falling has occurred by tufts 

 of reeds or bulrushes, associated or isolated, and sometimes followed 

 inside by the yellow water-lily and Potamogeton perfoliatus. The 

 turf-lakes with abrupt, sometimes sharply-sloping margins differ 

 in having a very narrow littoral zone, consisting of the Bog-bean, 

 {Menyanthes), the reed mace (Typha), Cladium, the reed, and the bul- 

 rush, while the yellow water-lily reaches almost to the edge. The 

 floor is generally carpeted, to a great extent, with myriophyllums and 

 charas, together with, in some lakes, the hornwort, the two mosses 

 above mentioned, Nitella and others. 



Shallower lakes with muddy or marshy banks with but a slight 

 incline, and alternately swamped or exposed, show a very variable 

 vegetation. In some can still be seen the littoral zone, the yellow 

 water-lily zone, and a bottom covered with myriophyllums and 

 charas ; in others mare's-tail and water milfoil clothe the whole 

 lake, while scattered patches of Nuphar, Polygonum amphibium, and 

 others are seen at the surface. 



Classification of Conifers. 



The most recent issue of the Linnean Society's Journal (vol. xxx., 

 no. 205) contains some valuable notes by Dr. Masters on the genera 

 of the two large orders of Gymnosperms, Taxaceae and Conifera?. 

 The observations are the outcome of a comparative examination of 

 the morphological characters of all the genera as far as was possible 

 in living plants, while the available museum and herbarium specimens 

 have been studied as well as the literature. Dr. Masters is well- 



