106 
white. A beautiful, variegated-leaved plant, altogether smaller 
and more elegant than P, tenax. (R. H. 1878, 56. 
P. Forsterianum (Forster's). A synonym of P. Cookianum. 
ee Pate Pe 
— 
d ) Flax. f. yellow or red, 
but variable, 2in. lo August. J. from 3ft. to 6ft. or more in 
length, rigid, erect, dark green, with a narrow, reddish-brown 
et e. and always split at the tip when old. 1798. The 
hardier of the two species. See Fig. 124. (B. M. 3199.) The 
following are some of the best forms: 
P. t. atro-purpureum (dark purple) Z. wholly of a beautiful 
purple, suffused with a reddish tinge. A handsome form, 
differing from the type only in the colour of its leaves, 
P. t. nigro- (black-spotted). J. green, about 
long and din. wide, narrowly edged . tho 
edge becoming broader and more distinct on the base, where it 
forms a conspicuous, zigzag line, elegantly spread out as the 
ts become mature. A compact-growing form, much dwarfer 
in habit than the type, and smaller also in the foliage. 
P. t. variegatum (variegated).* l. dark pan striped with ri 
yellow and white, often 6ft. in length. 8 A —— 
pretty, striped form of the common species. 
P. t. Veitchlanum (Veitch’s). A fine form, with shorter and 
narrower leaves, which are of a bright pea- green, and have broad 
stripes of a creamy-white, extending the entire length of each leaf. 
PHORODON HUMULI. This insect, known also 
as the Hop Aphis, is frequently most destructive to the 
Hop-plants, whore these are cultivated on a large scale; 
but in gardens it does little harm, though occasionally 
hurtful to Hops grown for ornamental purposes. It 
belongs to the green group of Aphides, and the genus 
differs very little from the other Green Flies in appear- 
Fig. 124. PHORMIUM TENAX, showing Habit and detached Flower. 
ance. Many efforts have been made to combat this pest 
in the Hop-gardens. One remedy is to wash the plants 
thoroughly, with the help of a garden engine, with a solu- 
tion of 3lb. or 4lb. of soft soap in 
200 gallons of water, adding a 
little infusion of coarse tobacco 
to the solution if thought fit; 
another is furnished by a newly- 
discovered emulsion of petroleum, 
which is said to be very effective. 
In gardens, it is only necessary 
to look occasionally to the young 
shoots, and to crush the Aphides 
before they become numerous. 
What is regarded by most 
entomologists as a variety of 
this insect (P. Humuli, var. 
Mahaleb) occurs in gardens on 
leaves of Plums, and also lives 
on Sloes. Among the most use- 
ful assistants in reducing the 
ravages of these, as well as of 
other Aphides, are the larve of 
Ladybirds (Coccinella septem- 
punctata, &c.), of Golden-eyed 
Flies (Chrysopa); and of Hawk- 
flies (Syrphus). 
PHOSPHATES OF LIME. 
Chemical substances which con- 
tain the elements calcium and 
phosphorus, both of which are 
found to be present in all 
plants. The ash which remains 
when the plants are burned 
invariably contains them in 
greater or less amount. Ex- 
periments on plants which are 
supplied with food of definite 
and strictly-ascertained composi- 
tion, have proved that when 
either of these elements is with- 
held, the plants remain small 
and stunted, though the other 
elements required in the food 
are all supplied. On adding 
the missing element to the food, 
growth begins, and goes on in 
a healthy way. But, though this 
has been ascertained, there is still much uncertainty as 
to the way in which each of these elements exerts its 
beneficial action on plants. It is believed that calcium 
is of use both in enabling plants to obtain the sulphur 
and phosphorus that they require more readily in com- 
bination with it (in sulphate of lime and Phosphates of 
Lime) than these elements could be otherwise supplied 
to them, and in combining with oxalic acid, which is 
largely formed in growing tissues of plants, but is 
hurtful to them im excess. The calcium unites with 
this to form oxalate of lime, in the shape of small 
crystals, called “ raphides, which are very common in 
the cells of many plants—in some resembling bundles of 
minute needles; in others, in the form of cubes; in 
others, like balls, studded over with sharp points. 
Oxalate of lime is harmless to plants, Phosphorus is 
believed to be of value chiefly in helping to form proto- 
plasm, and to transfer it from place to place, as 
needed for growth in the plants. Phosphates are em- 
ployed chiefly to supply phosphorus, and they are drawn 
from the soil by the plants as they require it. There 
are several Phosphates that contain calcium. They differ 
from one another in the percentage of calcium that they 
contain, and also in their solubility; but, for a discus- 
sion of their composition and preparation, the reader 
