798 



BOTANICAL PKESS. 



the case" of tlie field-boards already mentioned), closely glued together, 

 and firmly secured by small screws along the edge, at intervals of 

 three inches. They may be rounded on their outer margins. For 

 every two reams of drying paper not less than ten boards should be 

 procured ; two of which are for the outside and eight for the inside. 

 Sheets of stout pasteboard are also useful for packing up the plants as 

 they become dry. The pressure is best applied, on a botanical excur- 

 sion, by means of a rope put crosswise round the boards and paper, 

 and tightened by a rack-pin. This is much better than straps, which 

 are apt to give way, and are with difficulty replaced during an exom-- 

 sion. In other circumstances, pressure is best applied by means of 

 heavy weights. ;".^ The pressure ought not to be less than 100 lbs. 

 This is preferable to a screw-press, in which the pressure is not kept 

 up while the plants are losing their moisture. In order to allow free 

 ventilation, and thus to dry plants more rapidly, Mr. Twining recom- 

 mends, instead of boards, frames made of crossed bars, with spaces 



Fig..S61. 



Fig. 962. 



between them ; the surface applied to the paper being flat, — the others 

 being ribbed by means of prominent cross bars, so as to leave a venti- 

 lating space between the one frame and the other (figs. 961 and 962). 

 By an apparatus consisting of eight of such inner frames, and two 

 outer frames of a stouter nature, so as to bear pressure, the plants as 

 well as the paper may be dried rapidly. The apparatus, with paper 

 and plants firmly strapped, is suspended in a draft of air coming 

 through a partially closed window, or on the branch of a tree in sun- 

 shine ; and it is said that desiccation of the plants and paper is 

 accomplished in four days. By the use of artificial heat in an open 

 and airy place, as, for instance, by being placed before the fire, the 

 drying maybe accomplished in twenty-four or forty-eight hours. Mr. 

 Twining, when in Switzerland, first pressed the plants tightly for 

 twenty-four hours, and then piled them properly in the frame-work 

 apparatus, which was hung up in the hot air of a drying-room, and in 

 twenty-four hours more they were ready for packing, the paper also 



Kg. 961. Frames formed of^ cross-bars, forjprcssure and ventilation. |Fig. 962. Side 

 ■view of frames. One of the frames, a, seen laterally, with its cross bars forming projections ; 

 two of these frames, 6 and c, appear together, so as to; allow ventilation between them. 



