2046 



A TEXTBOOK OF THEORETICAL BOTANY 



scaly, woody stems. The flowers are dioecious and are borne on large 

 inflorescences. Nolina contains twenty-five American species and is 

 interesting because of the large tuberous base of the stem. 



In the Phormideae we have plants of smaller stature arising from a 

 rhizome. The leaves are radical and the flowers are hermaphrodite or 

 sometimes unisexual by the abortion of the stamens. The perianth segments 

 are connate. There is only one genus, Phormium, with two species in New 

 Zealand. P. tenax furnishes New Zealand Flax (Fig. 1985); it is sometimes 

 cultivated in gardens because of its ornamental leaves which somewhat 

 resemble those of an enormous Flag Iris. 



The Agavaceae are interesting anatomically on account of the peculiar 

 type of secondary thickening of the stem caused by the activity of a cam- 

 bium which produces fresh vascular bundles. This type of secondary 

 thickening occurs in Yucca, Dracaena, Cordyline and a few other genera. 

 The leaf anatomy also may show peculiar modifications associated with the 

 xerophytic condition which is especially well shown in Phormium tenax. 



Besides those already mentioned, many species, especially of Agave, are 

 cultivated in the warmer parts of Britain. Particularly fine collections may 

 be seen in the gardens of Tresco Abbey in the Scilly Islands. One of the 

 most striking species is A. americana, the Century Plant, whose inflorescence 

 may reach over 20 ft. in height. These plants take many years to flower, for 

 they grow very slowly, but once the magnificent inflorescence has been 

 produced the plant becomes exhausted and dies, though young ones may 

 develop as suckers from its base. Some of the smaller Agaves may flower 

 repeatedly year after year. 



PALMALES 



The Palmales are Monocotyledons often of large size. The stem is 

 fibrous and ranges from a minute almost vestigial structure to a very tall, 

 woody trunk. A few are climbers. The stem is usually clothed by the 



a6 



Fig. 1986. — Chamaerops /iiniiilis. Palmaceae. A, Male 

 flower. B, Hermaphrodite flower. (After Le Maout 

 and Decoisne.) 



persistent bases of the leaves which are often of enormous size. In some 

 species the trunks are armed with large spines formed in many cases from 

 adventitious roots. The leaves may be entire or pinnately divided and the 



