714 ERECT FOLIAGE STEMS. 



only 4 metres high, ami there even exist palms whose caudex barely rises above 

 the ground. 



The caudex of tree-ferns and cycads also remains comparatively short. When 

 travellers speak of the gigantic trunks of tree-ferns, they only mean gigantic in 

 comparison with the stems of the ferns growing in our European forests, which 

 either never appear above the ground, or like those of the ostrich fern {Stridhiop- 

 teris germanica), only 10 cm. above the soil. The New Zealand tree-fern Dicksonia 

 antarctica, with a diameter of 40 cm. reaches a height of 15 metres, and the caudex 

 of Alsophila excelsa, with a thickness of 60 cm., is 22 metres high. The cycads 

 scarcely ever reach this height, nor do the various other flowering plants possessing 

 a caudex, such as the species of the genera Yucca, Draccena, Urania, Pandanus, 

 Aloe, and Xanthorrhaa. The celebrated Dragon-tree {Dracceina D-Aico) of Orotava, 



1 whose age is estimated to be 6000 years, has a circlimference' of ll, and a height of 



, 22 metres. 



The caudex is in most cases simple, but several Pandanese and dragon-trees, and 

 among the palms, the Doum Palm (Eyphcene thebaica) growing in the Nile valley 

 and Hyphcene coriacea, fork and develop a few short branches when their main 

 caudex has attained a great age. Many caudices, e.g. those of the tree-fems Dick- 

 sonia antarctica and Todea barbata are completely covered with short aerial roots, 

 in consequence of which their surface has a peculiar bristling appearance. Many 

 caudices are also abundantly provided with thorns. For the appearance of most 

 of them it is of importance whether the dead leaves break oft' above the base, so 

 that the leaf-sheaths persist, or whether the leaf-sheaths are detached with them, 

 only a scar being left on the caudex. In the former case the stem is clothed some- 

 times with ridges or scales, sometimes with a fibrous integument, or even with dry 

 stumps. In the latter case it is covered with circular or shield-like scars. The 

 caudex of Caryota (cf. fig. 74, p. 811) becomes quite smooth after the leaves have 

 fallen off", and looks like a gigantic culm; indeed, it forms a link between the caudex 

 and that kind of stem which is termed a culm. 



The stem-structures which are comprehended under the name cidm (cwlmus) 

 difier in size even more than does the caudex. They may be classified in the follow^ 

 ing groups, which, of course, are not sharply marked oflF from one another. First, 

 the culm in the narrow sense of the word, which embraces those forms whose stem 

 does not exceed a diameter of | cm.; then the reed, which is not branched, whose 

 internodes are always surrounded by long sheaths, and whose stem has a diameter 

 of ^-5 cm.; and, further, the bamboo, which divides into numerous branches, having 

 short leaf-sheaths and a very peculiar anatomical structure; this will again be 

 referred to in the next chapter. The culm exhibits its highest proportions in 

 bamboos, especially in the species represented in fig. 172, which attains to a height 

 of 25 metres and a thickness of more than half a metre. From this extreme, on the 

 one hand, to the delicate little culm 2-3 cm. long, of many annual grasses of the 

 Mediterranean flora, there exists an unbroken series about the middle of which comes 

 the Southern Reed (Arundo Donax) with a height of 4 m. and a diameter of 5 cm. 



