THE HIGHER CRYPTOGAMIA. 275 



variegatum and palustre the number of cells in the diameter 

 of the pith is only 6 ; in vigorous shoots of Eq. limosum it 

 is 40. The number of leaf-tips and vascular bundles 

 appears not less variable ; in the main shoots of Eq. varie- 

 gatum it is 7 ; hi Eq. palustre 7 — 10; in Eq. pratense 10 ; 

 in Eq. limosum 10 — 20. Most striking differences in this 

 respect are found even in the axes of different orders of one 

 and the same shoot. 



The connexion between the cells of the pith of all the 

 indigenous (German) species of Equisetum is very soon 

 dissolved. The numerous intercellular spaces become filled 

 "with air. The cells of the pith are soon unable to keep 

 pace with the longitudinal growth of the periphery of the 

 stem. All connexion between the pith-cells ceases, they 

 are torn from one another, they become shrivelled, and in a 

 short time disappear altogether with the exception of a flat 

 double layer of cells in each internode which lasts as long 

 as the stem itself. Thus there is produced in each inter- 

 node a central pith-cavity covered above and filled with 

 air, having smooth side walls and a base rough with the 

 debris of the pith- cells. In just the same way- — by the 

 separation of a string of cells from the adjoining tissue, 

 by the early cessation of the multiplication of these cells, 

 and by their shrivelling and desiccation — an air-cavity is 

 produced, in Equisetum limosum, around each vascular 

 bundle; and ultimately by the decay of the central por- 

 tion of the vascular bundle, a narrow air-cavity is formed 

 in the interior of each of them. 



Normally, the terminal bud of the Equisetaceae never 

 ramifies. There is hardly any other group of plants which 

 exhibit such a well-defined, exclusively apical, growth. 

 Ramification is caused solely by adventitious buds. 

 These are produced in definite positions, viz., in the an- 

 nular locus of insertion of the sheathing leaf ; each adventi- 

 tious bud, with rare exceptions, being seated under the 

 angle between each two leaf-tips. The rudiment of the 

 adventitious bud appears long before that of the vascular 

 bundles of the same internode. In the autumn shoots of 

 Eq. pratense which are developed in the following spring, 

 a cell, situated in the defined position at the base of the 



