IN EXTRA-TROPICAL COUNTRIES. 265 



Populus tremuloides, Michaux. 



The North American Aspen. Ascends to Alpine elevations of 

 10,000 feet. The wood is white, soft, and readily worked, and can 

 be converted into paper pulp. Height 50 feet. It extends westward 

 to California, where also a particular species, P. trichocarpa 

 (Torrey), occurs. All Poplars might be planted, like all Willows, 

 in gullies, to intercept forest fires ; also generally on river banks. 



Porphyra vulgaris, Agardh. 



Temperate and cold oceans. This largely cosmopolitan seaweed is 

 mentioned here, because in Japan it undergoes regular cultivation. 

 For this purpose branches of Quercus serrata are placed in shallow 

 bays, where Porphyra occurs, during spring, and the crop is 

 obtained from October to March, the seaweed being consumed in its 

 young state. It grows best where fresh water enters the sea. 

 Porphyra contains about 26 per cent, of nitrogenous substances 

 (with more than 4 per cent, of nitrogen) and about 5 per cent, of 

 phosphate of potash. In Japan, according to the catalogue of the 

 International Exhibition of Sydney, the following Algae are also 

 consumed for food : Glaepeltis intricata, G. capillaris, Laminaria 

 saccharifera, two species of Phylloderma, Phyllitis debilis, Kallhy- 

 minia dentata, Capea elongata, Alaria pinnatifolia, Gracilaria con- 

 fervoides, Enteromorpha compressa, species of Cystoseira and 

 Halochloa, Codium tomentosum, Mesogloia decipiens, and Gelidium 

 corneum. 



Portulacaria Afra, Jacquin. 



South Africa. Called Spekboom. Affords locally the principal 

 food for elephants ; thus this succulent shrub may deserve 

 naturalization on stony ridges and in sandy desert land, as likely 

 nourishing to sheep. 



Pouzolzia tuberosa, Wight. 



India. The turnip-shaped root of this herb is edible. The plant 

 may prove hardy here, and its root improve in culture. 



Prangos pabularia, Lindley. 



Plateaux of Mongolia and Thibet. A perennial fodder-herb, much 

 relished by sheep, eligible for cold and arid localities and deserving 

 naturalization on Alpine pasture-grounds. Other perennial species 

 exist near the Mediterranean Sea, on the Atlas, the Caucasus, and 

 the Indian highlands. P. pabularia is regarded by some as the 

 Silphium of Arrianus. 



Pringlea antiscorbutica, W. Anderson and R Brown.* 



The Cabbage or Horse-radish of Kerguelen's Island. The perennial 

 long roots taste something like horse-radish. The leaves in never- 



