107 



99 



purposes/ As tlie paper absorbs moisture it becomes less efficient, 

 and tins tendency may be counteracted by placing the specimens 

 between layers of several sheets of paper, but it is better to 

 change the damp papers frequently, and the oftener this is done 

 the more quickly will the specimens become dry.^ Specimens 

 under pressure, however, except those that are particularly rigid, 

 soon become limp and their more delicate or succulent parts tend 

 to curl up when they are transferred from the damp to a dry 

 sheet of paper, and therefore have to be straightened and 

 flattened out again. As this operation cannot always be success- 

 fully performed and in any case involves a waste of time, the 

 difficulty may be overcome by placing each specimen in a folded 

 sheet of thin"^ paper (''retainer"), leaving it there until it is dry 

 and changing only the intervening sheets of stouter or more 

 absorbent paper (''pads or driers'') as often as may be neces- 

 sary. To facilitate the changing of the '^pods," the dieets 

 making them up should be stitched together and be of a colour 

 different from that of the "retainers/' Should fuller padding 

 be necessary for more bulky or succulent plants tw^o pads of 

 " driers" may be used between each pair of "retainers." The 

 use of easily distinguishable "retainers" or "pads" has the 

 further advantage that the changing of the paper becomes a 

 purely mechanical procedure which can be entrusted to un- 

 skilled hands, particularly when the free edges of the "retainers" 

 are pinned together or folded over so that the sj^ecimens or loose 

 parts cannot slip out. To ensure the full action of the "pads 

 they must, of course, be perfectly dry when taken into use, and 

 if they are at the same time moderately warm, they will be still 

 naore effective. If well dried after each change they can be used 

 over and over again. How to dry them must, of course, depend 

 on circumstances. The sun may do it one day, w^hilst artificial 

 heat and ventilation may have to be resorted to the next day. 



Packets containing fresh specimens must not be placed im- 

 mediately on others with plants already half dry. They should 

 be either kept apart or a broad sheet of millboard should be 

 inserted between them. Similarly, slowly drying specimens 

 should be made up in separate packs with more ample padding. 



Quite apart from the action of absorbent paper under pressure, 



the process of drying can be accelerated by applying heat and 



ventilation to increase evaporation from the packs containing the 



specimens; but if artificial heat be used, care must be taken that 



the drying is not carried so far as to make the specimen?? too 



brittle. Good results are obtained if small packs are hung up in 



the sun or over a fire, and if the driers are also frequently 

 changed. 



The pressure. — Pressure may be applied in various ways. It 

 should be light at first, but be increased more or less rapidly as 

 the^ specimens become dry, so as to prevent undue shrinkage or 

 shrivelling. At the same time it must never be carried so far 

 that the softer or more delicate parts are in danger of being 

 crushed or of becoming glued to the paper. In fact, the collector 

 may make it a rule that too little pressure is less harmful than 



