280 HOFMEISTER, ON 



followed by division by means of septa parallel to the basal 

 surface, and perpendicular to the longitudinal axis of the 

 root. The outer cells of the group formed by the multi- 

 plication of those cells of the second degree which are 

 directed upwards (those which adjoin the daughter-cells of 

 the second degree which are directed downwards) continue 

 to multiply for some time by division by means of septa 

 alternately radial and parallel to the periphery. But the 

 succession of these divisions is twice interrupted by the 

 formation of horizontal septa in the entire mass of cells pro- 

 duced by the multiplication of the cell of the second degree 

 which is directed upwards. 



The adventitious roots like the adventitious buds are 

 capable of remaining dormant for a long time. When they 

 burst forth and become elongated, the central string of cells 

 is transformed into a vascular bundle. The tissue immedi- 

 ately enclosing the latter becomes disintegrated, dries up, 

 and ultimately disappears. Thus a hollow cylindrical air 

 cavity is produced beneath the bark of the adventitious 

 root. The upper surface of the root becomes covered with 

 long papillae which become brown in age. In very old 

 rhizomes the cortical layer of the root usually disappears 

 entirely; the central vascular bundles only, (whose tissue 

 is very firm) are persistent, and have the appearance of 

 tough, thick, deep-brown fibres. 



Fruit is usually developed only on the vigorous shoots 

 produced from the lowest internodes of a shoot of the 

 previous year. The transition from the form of the ordinary 

 sheathing leaves, to that of the lowest circle of sporangia is 

 very rapid and sudden, even in those species which (like 

 Equisetum arvense) have special fructifying shoots. The 

 sheathing leaf immediately underneath the fruit is shorter 

 and more fleshy than the others ; there is no other inter- 

 mediate condition. The fructification is morphologically 

 unlimited ; owing to its mode of origin its longitudinal 

 development is not confined within bounds, any more than 

 that of the vegetative shoots, which (at least those above 

 ground) nevertheless do not become elongated beyond a 

 certain extent. Each circle of sporangia makes its appear- 

 ance in the form of an annular cushion underneath the 



