51 
called “mosaic disease” of Tobacco plants and of 
Tomatoes is supposed to be due to this cause, and certain 
experiments indicate that it is highly infectious. 
Most gardeners will have come across examples of 
abnormal formations in flowers. Often the sepals may 
become leafy as in Jack-in-the-Green Primroses, sometimes 
the petals have a leaf-like appearance as in the Green Rose. 
To the flower-lover these transformations are more curious 
than beautiful, but to the botanist they are of considerable 
interest as cases of reversion. For we must assume that 
the various Horal organs are all modifications of leaves 
which have become adapted to the special function of 
reproduction, and in such foliaceous developments we may 
see a retrogression to a more primitive type of leaf. More 
rarely, but still occasionally, we may find stamens or pistil 
becoming transformed into vegetative leaves; the latter is 
often the case in the flowers of the Double Cherry. In both 
cases sterility of the flower is caused. In other sports the 
outermost leaves of the flower, the calyx, may become 
coloured and delicate in texture like the corolla. This is 
the condition in the hose-in-hose variety of the Polyanthus. 
More frequently it is the inner leaves of the flower, the 
stamens, that become petaloid. The “doubling” of 
flowers is sometimes found to take place in wild plants 
when transplanted into garden soil. In all probability 
the tendency to doubling is independent of the cultivation 
of the plant, but the rich nutrition which the plant receives 
accentuates the effect. Certainly double varieties to be 
kept in perfect condition require an abundant supply of 
food, and are liable to degenerate when grown in poor soil. 
Degenerate is perhaps not a good term to use, as the plant 
is in a more perfect condition from the reproductive point 
of view when the stamens and pistil are normally 
develqped and fertile than when they are transformed into 
showy petals. In that case the flower is generally com- 
riteeely sterile, though it may sometimes retain a few 
serviceable stamens or a receptive seed vessel. 
From the doubling of flowers such as the Rose, we must, 
distinguish the doubling of the so-called “flowers” of 
Daisies, Chrysanthemums, and other members of the Com- 
posites. In this Family the apparent flower is really a 
head of small flowerlets or florets closely crowded to- 
gether. These are often of two kinds, showy ray florets 
and small central disk-florets usually of a different colour. 
