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 stem (PI. 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 Bq. 



