52 



When these "flowers" are said to double, it is by trans-- 

 formation of the tubular flowers of the centre into con- 

 spicuous strap-shaped flowers, like those of the margin of 

 the inflorescence. In that case they need not necessarily 

 become sterile, for in many Composites like the Dandelion, 

 all the florets are normally of the ray-floret type. Another 

 curious freak met with in some of the Composite when 

 they receive abundant nutrition is the development of some 

 of the ray-florets into small heads of flowers on stalks of 

 their own, so that the large central head is surrounded by 

 a number of lesser ones. This is the condition in the 

 Hen-and-Chicken Daisies, and similar modifications are 

 found in other plants. 



A not uncommon abnormality in gardens is the 

 development of a terminal flower of large dimensions and 

 regular shaped at the top of the flowering spike of the 

 Foxglove; in the Snap Dragon, too, flowers showing radial 

 symmetry instead of the usual tw r o-lipped condition may 

 be formed. A plant may indeed bear nothing but 

 " peloric " flowers as these are called. 



Monstrosities may also occur in the development of 

 fruits. Double-fruited oranges with two whorls of carpels 

 (pegs) one inside the other are occasionally found, while 

 in one variety known as Buddha's fingers, the various 

 carpels are only united below and taper off above into 

 finely divided pod-like segments. 



While most of these malformations are due to little 

 understood internal causes, many cases of excessive devel- 

 opment of plant structures are produced as the response 

 to irritation. Thus, numerous kinds of galls and tumours 

 may be developed by animal and. vegetable parasites, 

 insects and fungi, which injure the tissues and cause them 

 to swell or grow more vigorously. These will be dealt 

 with in later chapters. 



Plants like animals have the pow r er of protecting them- 

 selves against external injury and of healing any wounds 

 that, are caused thereby. The most usual method is by the 

 formation of layers of cork, which will protect any exposed 

 part from the atmosphere, thereby preventing the excessive 

 loss of moisture through the wounded surface and also 

 reducing the chances of invasion of the tissues by disease 

 or decay producing organisms. This development of a 

 resistant layer of cork is due to the active growth of the 

 living cells of the plant in the exposed region. This active 



