i8o2 A TEXTBOOK OF THEORETICAL BOTANY 



develop their own cambia and form secondary wood independently of one 

 another (Fig. 1695). Tendrils are axillary and represent modified axes of 

 inflorescences which fork at their apices, the branches being flattened and 



Fig. 1695. — Serjania sp. Transverse section 

 of an old stem with four distinct masses of 

 secondary wood, each developing from a 

 separate cambial ring. 



much inrolled. The internal tissues generally contain special cells which 

 secrete resinous or latex-like material. The flowers are unisexual though 

 bisexual flowers may occur in which the stamens are functionless. These 

 flowers show a tendency towards zygomorphy, are tetramerous or penta- 

 merous and are polygamous. The stamens are usually arranged in two 

 whorls and are often reduced to eight and inserted in a disc around the 

 ovary. The latter is trimerous and contains one ascending ovule in each 

 loculus. The fruit may be either a dry capsule or nut or a fleshy berry or 

 drupe. The seed may develop an aril and is non-endospermic. 



Serjania and Paiilliriia, with 175 and 121 species respectively, are two 

 important American genera both of which form lianas with watch-spring- 

 like tendrils. They both produce winged, dry fruits. 



Among species which are of some economic importance first place must 

 be given to Litchi chinensis (Fig. 1696). It has been cultivated in China for 

 at least 2,000 years. It is an ornamental tree growing to 40 ft. in height with 

 a broad round crown and light, glossy, green foliage. The flowers are small 

 and unattractive and the fruits are produced in loose clusters of from two to 

 twenty. Each is oval in shape, about i| in. in diameter. When ripe it is 

 rose-red in colour. The seed is large but is surrounded with a translucent 

 fleshy mass which is really an aril. It has a white, juicy consistency and 

 a flavour resembling a grape. The total sugar content is about 15 per 

 cent. 



Very similar in structure is the genus Nephelium which contains about 



