322 Transactions. — Botany. 



urged against the screw-press that the pressure becomes 

 relaxed as the moisture is extracted from the specimens. 

 This, however, is theoretical rather than practical. As a 

 matter of fact, when a press receives proper attention, and 

 the wet sheets are replaced by dry ones — say, on alternate 

 days — the pressure is not perceptibly relaxed : even if it 

 were necessary to leave the press unchanged for several 

 days, nothing would be more easy than to give an occasional 

 turn of the screw. 



A simple but effective portable screw-press which I have 

 had in use for over forty years is made of Jin. square iron, 

 forming a frame HJ-in. wide by 12in. in height ; the middle 

 portion of the upper side is enlarged and perforated with a 

 chased aperture to receive the screw, which is from Gin. to 

 7in. long (including the head), and terminates in an obtuse 

 point below. The exact weight of a press ll-|in. by 12in. is 

 51b. ; a smaller size might be made out of fin. square iron. 

 A press of this kind never gets out of order, and is almost un- 

 breakable, while it is quite as portable as a strap-press. Two 

 of these portable presses may be carried on a pack-horse, 

 leaving ample space between them for the tent and other field 

 impedimenta. On Plate XXVIa. is shown the form of the 

 press and the way in which it is used. 



The amount of pressure required varies with the nature of 

 the specimen. Many ferns and slender grasses, such as Poa 

 trivialis and Microlana stipoides, do not require more than 

 from 201b. to 301b., but twice this weight would not be too 

 much for robust kinds such as Arundo conspicua, Danthonia 

 flavesccns, &c. From 501b. to 801b. is sufficient for most 

 herbaceous and for many woody plants, while from 801b. to 

 1001b., or more, may be used for the larger species of Aciphylla 

 and for stout, wooded plants with thick leaves. Overpressed 

 specimens are often useless for examination. 



With regard to the number of changes of paper and the 

 length of time required for drying different plants, it is hardly 

 possible to lay down hard-and-fast rules, as so much depends 

 upon the state of the atmosphere. Slender grasses and ferns 

 require but two or three changes, and may often be dried in a 

 week or ten days ; most plants, however, require at least a 

 fortnight ; thick-leaved and fleshy plants require three or four 

 weeks, or longer. Submerged aquatic plants dry very quickly 

 after the second or third change. But in these and similar 

 matters a little practice and observation are of more value than 

 much teaching. 



Instead of solid boards for the top and bottom of the press, 

 and for dividing it into sections, ventilators are sometimes em- 

 ployed. These may be made in various ways — say, of two in- 

 terrupted layers of bars iin. square of any common wood, the 



