274 IIOFMEISTER, ON 



joint is thus produced. At the time when the annular 

 vessel becomes continuous a multiplication commences in 

 the neighbouring cells those situated in front (towards 

 the outside) and to the side by means of vertical septa 

 alternating with radial septa and with septa parallel to 

 the periphery of the stein (PL XXXVI, fig. 1). Thus a 

 thick string of cambial cells is produced in which more 

 annular vessels (with much narrower rings) are shortly 

 afterwards formed in a similar manner, and where at a 

 much later period spiral vessels are also formed. In the 

 developed internode this string of cells represents a closed 

 vascular bundle. 



The tips of each leaf and the corresponding vascular 

 bundles of each stem-joint alternate with those of the next 

 lower one. Soon after the first separation of the vascular 

 bundle from the surrounding tissue of the stem which 

 separation takes place whilst the vascular bundle has still 

 the appearance of a string of cambial cells and exhibits 

 only a single annular vessel on its inner side the cells of 

 the node from the base of the vascular bundle as far as 

 the two adjoining ones of the next lower stem-joint are trans- 

 formed into short spiral cells arranged in a moniliform 

 manner ; the cells which adjoin these strings in a lateral 

 and outward direction are transformed into a thin layer of 

 cambial cells which at a later period also take part in the 

 formation of vessels. 



After the commencement of the formation of the vascular 

 bundle of the stem the corresponding leaf-tip exhibits the 

 transformation of a string of cells into a vascular bundle 

 traversing its median longitudinal line. The first vessels 

 which appear in the leaf are elongated, narrow, spiral 

 vessels. The vascular bundles of the leaf attain only a 

 slight thickness. 



The distance from the middle point of the stem at which 

 the formation of vascular bundles commences in other 

 words the bulk of the pith and the number of leaf- tips and 

 the (corresponding) number of the vascular bundles of the 

 internode which bears the leaf is very variable according 

 to the activity of the growth of the shoot, and according to 

 the number of its diametral cells. In thin shoots of Eq. 



