INTRODUCTION. 1 9 



It is best to mount Desmids in the liquid in which 

 they have been preserved, and old gold-size is the onlv 

 safe varnish for sealing them up. The first coat of 

 gold-size should be allowed to thoroughly dry before 

 another one is put on. Sometimes an exceedingly 

 thin, well-seasoned cell of gold-size is used in which 

 to mount them. This cell must be prepared months 

 beforehand by making a thin ring of gold-size on the 

 slide. Nothing can equal these fluid mounts for 

 purposes of future examination, but even the best of 

 them frequently dry up. They may be mounted in 

 glycerine jelly, and with great care the larger species 

 can be placed in any desired position, but specimens 

 mounted in this medium often exhibit considerable 

 distortion. 



The surest way of becoming acquainted with the 

 diagnostic features of Desmids is to draw them very 

 carefully in all positions. As previously stated these 

 drawings should be made to scale by means of a 

 camera lucida. This is also the best means of obtain- 

 ing accurate measurements of the plants. The draw- 

 ings can be finished off by direct observation, but the 

 outline and the precise disposition and form of the 

 markings must be drawn by means of the camera, in 

 order to ensure exactitude. Needless to say some 

 years of practice and experience are required before 

 faithful representations of the smaller Desmids can be 

 made. Strong fine drawing-paper should be used, 

 and the only useful pencil is the "HHHH," sharpened 

 on the finest emery paper. The drawings should be 

 fixed on to stiff sheets of paper of uniform size, each 

 sheet being devoted to one species. In this way the 

 variations of a species can be best seen. 



In conclusion, we must remark that this group of 

 microscopic plants is well worth studying, and we 

 sincerely hope that the appearance of our work will 

 attract the attention of students to this beautiful and 

 somewhat neglected family of plants. During a 



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spring or a summer holiday, sufficient material can be 



