. Elements of plant anatomy;. Botany -- Anatomy. ANATOMY OF TISSUES. 123 details, but a general description of the beginning of the bundle cylinder and its subsequent development may be given as follows. The origin of the root bundle differs in several respects from that of the stem. This may be illustrated by a cross-section near the root tip where there are four xylem plates. At their first appearance they consist of four cambium strands similar in character to those described in the stem, that is, they are com- posed of long, small, sharp-pointed cells arranged in groups each of which prese
. Elements of plant anatomy;. Botany -- Anatomy. ANATOMY OF TISSUES. 123 details, but a general description of the beginning of the bundle cylinder and its subsequent development may be given as follows. The origin of the root bundle differs in several respects from that of the stem. This may be illustrated by a cross-section near the root tip where there are four xylem plates. At their first appearance they consist of four cambium strands similar in character to those described in the stem, that is, they are com- posed of long, small, sharp-pointed cells arranged in groups each of which presents an oval circumference on the cross-sec- tion. These four ovals may meet at the centre, in which case there is no pith formed. The first appearance of xylem is pro- duced by certain of these cells turning into lasting tissue of the nature of xylem. This development or change proceeds at first toward the centre, and continues until the entire central portion is occupied by xylem, a large portion of which consists of ducts. The extreme outer portion of the cambium string remains meri- stematic and after the xylem at the centre is completed or during this time, it continues to develop or cut off ncAv cells toward the centre, which are also in time turned to xylem tissue. Between the plates of xylem the cells do not at first grow into cambium cells to give rise to phloem plates, but remain parenchymatic. They do, how- ever, become meristematic, cutting off new cells so that the section which they compose keeps pace with the radial increase in the xylem plates. The first appearance of phloem is caused by some of the cells of the outer portion of these sections changing gradually into phloem elements, chiefly sieve tubes, but these are often accompanied by bast cells. (Fig. 53.) This gives an approximate idea of the manner of origin of a radial bundle. In roots where a pith occurs the process is. Fig. 53. a a represent the cam- bium bundles from which are derived the first xylem p
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotanya, bookyear1895
