BOTANICAL GAZETTE. 67 



pose very well. Mr. Ward's advice, however, will not encumber the 

 most precise disposition. The writer must confess that he has about 

 the same feeling in regard to this whole subject as he has expressed 

 in the matter of microscopes. An herbarium, like a microscope, 

 should not be an end. but simply a means to an end, and 

 when it ceases to be that, it becomes a mere toy, like a col- 

 lection of postage stamps or crockery. It is to be feared 

 that the craze for collecting has infected too many of our 

 botanists whose whole enjoyment of their plants is the miser's en- 

 joyment of his gold. All the collecting that is being clone in this 

 country should yield us richer returns of information. _ Every her- 

 barium, however small, should be a perennial fountain and not a 

 stagnant pool. Mr. Ward enforces well the real object of an herba- 

 rium, but that part of his advice will be less heeded than the rnechan- 

 rical part. 



The Leaves of Aquatic Plants.— The leaves of aquatic- 

 plants may be divided into 3 classes; aerial, floating 

 and immersed. The first class has stomata on both sides 

 of the leaf; the second, on the upper side only; and the last class 

 has none at all. In the first two, the air can be taken through the 

 stomata directly into the leaf; in the last class, the necessary gases 

 not existing as a body (of air) in the water, there is no use for stoma- 

 ta, which would take up water as well as air. So we have breath- 

 ing holes in the leaves disconnected from direct contact with water 

 and into which carbon dioxide is absorbed for the use of the plant 

 (Box. Gaz., Vol. VI. No. 8). These are the well-known intercellular 

 spaces. So we see that it is a natural division. 



To the first class belong the leaves of the subaquatic or marsh 

 plants, which root in the water and send their branches into the air, 

 as in Nasturtium officinale. 



To the next belong the leaves of Nymphceacece. Limnanihemum, 

 Orontium and Marsilea, raised by petioles to the water surface, also 

 those of Schollera and Callitrichacece (aquatic forms) raised by 

 stems to the same level. The peduncles of some water flowers ar e 

 also elongated to get to the air. 



To the last class belong some Isoetes, Potamogetons, Vallisneria, 

 Ranunculus divaricatus, and most Utricular ice. 



Some plants combine the second and last classes, having 

 both floating and immersed leaves (some species of Potamogetoh). 



Some, the first and last classes, have both aerial and immersed 

 leaves, as Nasturtium lacustre and Myriophyllum. 



A few plants having stomata (first class) , beginning their exist- 

 ence in the water, emerge as the latter dries up. 



Plants of the second class, disconnected from the land and often 

 very small, are sometimes matted to keep the stomata-bearing sur- 

 face upward. This is effected in Azolla by its branching habit, in 



