82 



THE DICTIONARY OF GARDENING, 



Peronospora continued. 



zoospores ; and the smooth, unridged coat of the oospore, 

 distinguish this parasite of the Umbelliferce. 



8. P. ganglioniformis is parasitic on many Composites, 

 and among these is the Lettuce, to which it, at times, 

 does much harm. The fertile stems are somewhat 

 flattened and broad, bifurcated three to eight times, and 

 bear at their tips a flattened enlargement, like a nerve 

 ganglion (whence the specific name), on which, chiefly 

 round the margin, stand from two to eight short, slender 

 branchlets. Each of these bears a pale or colourless, 

 nearly round conidinm, provided with a minute wart 

 at one end, from which the mycelium tube is emitted 

 in germination. The oospore is yellowish-brown, its outer 

 coat being slightly wrinkled. 



9. P. pygmcea lives on Anemone nemorosa and on 

 Hepatica triloba, as well as, occasionally, on cultivated 

 Anemones. It is easily known by the fertile stems being 

 short and stout, and thickened upwards to a kind of 

 head, on which grow from two to six short, slender 

 branchlets. Each of these bears an ovoid or elliptical 

 conidium, which, in germination, gives out all the con- 

 tents, through a small wart at one end. The oospore 

 is pale brown, and has a smooth, wrinkled coat. 



The three following species may possibly occur in 

 Britain, though not yet recorded from this country. 



P. viticola is parasitic in North America, on the native 

 American Vines, and on the introduced European Vine. 

 It has not yet crossed the Atlantic, but may easily, be 

 brought on the Vines so often imported from America 

 to Europe, since it is abundant in the Eastern United 

 States. It grows on all green parts, and destroys them, 

 rendering them brown. The fertile stems are trifurcated 

 far more often than bifurcated, and end in crowded, short 

 branchlets, bearing elliptical conidia, which form zoospores. 

 The oospore has a smooth, yellow, thick outer coat. 



P. Cactorum causes decay and rottenness of the fleshy 

 tissues of cultivated species of Cactus. The fertile stems 

 bear a few branchlets, ranged along one side. The 

 conidia are colourless, ovoid or elliptical, with a con- 

 siderable wart on the tip, and through this the mycelial 

 filament emerges in germination of the conidium. The 

 oospore has a smooth, thick, pale brown outer coat. This 

 disease has been the cause of a good deal of injury in 

 botanic gardens in Germany. 



P. Schachtii has frequently proved very destructive to 

 Beets on the Continent. It forms a bluish-grey coat 

 on the lower surface of the leaves, which become yel- 

 lowish-green, wrinkled, and fleshy, and remain small. 

 Frequently, the young shoots and the heart-leaves are 

 destroyed. The fertile stems bear several short branches ; 

 the terminal branchlets are short, straight, blunt, spread- 

 ing, and bear ovate, dull violet conidia. The oospores 

 are unknown. The mycelium lives through the winter 

 in the diseased plants, and resumes its growth in the 

 young leaves during the following year. The seeds from 

 diseased plants are often affected as shown by the 

 appearance of the Fungus on the seedlings. 



The Potato-disease Fungus, frequently described under 

 the name of Peronospora infestans, Mont, (e.g., in Cooke's 

 "Handbook of British Fungi"), has, of late years, been 

 placed in a separate genus, under the name Phytophthora 

 infestans. For the characters distinctive of the genus, 

 and the habits of and remedies for P. in/estans, and of 

 the only other species, P. Fagi, see Phytophthora. 



FERSEA (a name applied by Theophrastus to an 

 Egyptian tree). Alligator or Avocado Pear. OBD. 

 Laurineae. An extensive genus (about 100 species have 

 been enumerated) of mostly stove trees or shrubs, all of 

 which (except one species from the Canary Islands) 

 are natives of tropical and sub-tropical Asia and 

 America. Flowers disposed in panicles ; perianth tube 

 short; limb segments six, almost equal, or the three 

 outer ones smaller ; perfect stamens nine. Fruit often 



Persea continued. 



large and fleshy. Leaves alternate or scattered, cori 

 ceous, penniveined, or more or less distinctly trip. 

 nerved. The undermentioned species is the only 01 

 introduced, and it is rarely seen in cultivation, 

 thrives best in a compost of loam and fibry peat. Pr 

 pagated, in autumn, by layers of the ripened shoots, c 

 in May, by cuttings of firm shoots, inserted in san 

 under a bell glass, in heat. 



P. gratissima (most-grateful). Alligator or Avocado Per 

 fl. green, about in. across, fr. pear-shaped, yellow and brow 

 often tinged with deep purple, and about 4in. long. I. elliptic! 

 narrow towards the base, about 6in. long. h. 25ft. to 30ft. We 

 Indies, 1739. The flavour of the fruit somewhat resembles th 

 of butter, or marrow, hence it is called " Vegetable Marrow " 

 the West Indies. It is so rich and mild that most people mal 

 use of some spice, or pungent substance, to give it poignanc' 

 and wine, sugar, lime-juice, but mostly pepper and saft, are use 

 Marks made with the stone of the seed on a white wall will t 

 as red as blood, and cannot be effaced until the wall is whit 

 washed, and even then only with difficulty. (B. M. 458 

 B. E. 1258.) 



FIG. 92. FRUITING BRANCH, LEAF, AND STONE OF PERSICA 

 DAVIDIAJA. 



PERSICA (so named in allusion to the Peach bein 

 supposed to come originally from Persia). Peach. OBI 

 Rosacece. A small genus of hardy or half-hardy fruit-trees 



