82 THE DICTIONARY OF GARDENING, 
Peronospora—continued. 
zoospores; and the smooth, unridged coat of the oospore, 
distinguish this parasite of the Umbellifera. 
8. P. ganglioniformis is parasitic on many Composite, 
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 conidium, 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. pygmea 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. Cactorwm causes decay and rottenness of the fleshy 
tissues of cultivated species of Cactus. The fertile stems 
„ 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. infestans, and of 
the only other species, P. Fagi, see Phytophthora. 
PERSEA (a name applied by Theophrastus to an 
Egyptian tree). Alligator or Avocado Pear. ORD. 
Laurinee. 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, coria- 
ceous, penniveined, or more or less distinctly tripli- 
nerved. The undermentioned species is the only one 
introduced, and it is rarely seen in cultivation. It 
thrives best in a compost of loam and fibry peat. Pro- 
pagated, in autumn, by layers of the ripened shoots, or, 
in May, by cuttings of firm shoots, inserted in sand, 
under a-bell glass, in heat. 
P. gratissima (most-grateful). Alligator or Avocado Pear. 
ji. green, about żin. across. fr. pear-shaped, yellow and brown, 
often tinged with deep purple, and about 4in. long. L. elliptical, 
narrow towards the base, about 6in. long. R. 25ft. to 30ft. West 
Indies, 1739. The flavour of the fruit somewhat resembles that 
of butter, or marrow, hence it is called ‘‘ Vegetable Marrow” in 
the West Indies. It is so rich and mild that most people make 
use of some spice, or pungent substance, to give it poignancy ; 
and wine, sugar, lime-juice, but mostly pepper and salt, are used. 
Marks made with the stone of the on a white wall will turn 
as red as blood, and cannot be effaced until the wall is white- 
washed, and even then only with difficulty. (B. M. 4580; 
B. R. 1258.) : i 
a \ 5 | 
Fig. 92. FRUITING BRANCH, LEAF, AND STONE OF PERSICA 
: DAVIDIANA. 
PERSICA (so named in allusion to the Peach being 
supposed to come originally from Persia). Peach. ORD. 
Rosacee. A small genus of hardy or half-hardy fruit- trees, 
