368 BOTAJ^T. 



mental tissues from node to node, parallel with, but inde- 

 pendeiit of, one another. At the nodes they split into two 

 branches, which unite right and left with corresponding 

 branches of other bundles, and thus form the bundles of the 

 next internode. The bundles of successive internodes thus 

 alternate with one another. Each leaf of the leaf-sheaths 

 sends down a bundle, which joins a bundle in the stem at 

 the point where two descending branches of contiguous bun- 

 dles from the upper internode unite to form a bundle in the 

 lower internode. The bundles are thus seen to be of the 

 "common" type — i.e., they are common to both stem and 

 leaves. As to their construction, they are collateral, and 

 contain tracheary, sieve and fibrous tissues (paragraph 139, 

 and Fig. 99). The remainder of the stem (the fundamental 

 portion) is made up for the most part of parenchyma ; in the 

 cortical portion of the vegetating shoots it contains an 

 abundance of chlorophyll, and it is here frequently pene- 

 trated by large longitudinal canals {I, Fig. 249) ; in the 

 medullary portion a great central canal soon appears by the 

 rapid growth causing a rupture of the tissues {h, Fig. 249). 

 There are frequently found in the hypqdermal portions of 

 the fundamental systems bands of thick-walled tissue, which 

 are either sclerenohymatous or fibrous. 



(a) This class contains but one living order, the EQtriSBTACBiB, hav- 

 ing the characters of tjio class as given above. In ancient geological 

 times the Calamites and their allies constituted a dietinct order, the 

 CalamariecB, now extinct ; they differed from the Equiaetacecs in hav- 

 ing fibro-vascular bundles which increased exogenously. The Cala^ 

 mariem were represented in the Devonian by a species of Aslerophyl- 

 liles. In the Carboniferous period there were many species of the gen- 

 era Calamites, Calamocladus, Ca'amostachys, Sphenophyllum, etc. In 

 the Permian the order became extinct. 



(6) The order Bquisetacem includes but a single genus, Equisetum, 

 which contains about tweuty-five species. None of the species attaiii 

 a great size, the usual height being from 20 to 100 cm. (8 to 40 inches) ; 

 one species {E. giganteum) in tropical South America attains a height 

 of 9 to 10 metres (30 feet or more), but it is very slender, being no more 

 than 30 to 25 mm. (1 inch or less) in diameter. The silicious stems of 

 E. hyemale, a common species, are sometimes used for scouring knives 

 and other articles. 



(c) The germination of the spores of Equisetinse may be studied by' 



