BOTANICAL COLLECTIONS 113 



showing the general topography of masses of vege- 

 tation. A standard collection, selected by a specialist, 

 of lantern slides of this character which could be 

 purchased in one set, would be of great value and 

 doubtless will soon be offered by some of the dealers, 

 who already offer heterogeneous lots. 1 The best 

 stereopticon is one using the arc electric light; it is 

 handier, cheaper, and better than the calcium and 

 other forms, and is so powerful as to need no elaborate 

 system of dark shades to the room, but may be used in 

 almost full daylight. Many forms of such lanterns are 

 offered ; I use to my satisfaction one made by J. C. 

 Colt, of New York. The best screen is a smooth white 

 wall. With such a lantern, and an ordinary microscope, 

 one may also project microscopic objects upon a 

 small screen, and thus show tissues, circulating proto- 

 plasm in Nitella, etc. ; but in general the manipulation 

 is so time-consuming and difficult that it is hardly 

 worth while unless one has a liking for that very 

 kind of thing. Where a lantern is impracticable, it 

 is still decidedly worth while to collect photographs, of 

 which many of value are now obtainable from return- 

 ing tourists and other sources. A superb collection 

 has recently been made available in Schimper's new 



1 A great number indeed, selected by Koch, is published by Kriiss in 

 Hamburg; a catalogue may be obtained from any dealer in botanical 

 supplies. Unfortunately, these are mostly but woodcuts from books, not 

 photographs from nature. Most American dealers in stereopticons also 



offer botanical slides. 



I 



