CARPOSPOREM. 



293 



From the carpospore of the fruit of Cbara^ the sexual leaf-forming plant is not 

 immediately developed, but a Pro-embryo precedes it, which attains only small dimen- 

 sions and consists of a single row of cells with limited apical growth. The stem of 

 the Leaf-bearing Sexual Plant springs from a cell which lies at some distance from 

 the apex of the pro-embryo and grows in a direction nearly at right angles to that of 

 its axis. The unlimited apical growth of the plant depends on an apical cell (Fig. 192, 

 C, t) from which segments are cut off by transverse septa. Each segment immediately 

 divides again by a transverse septum into two superposed 

 cells, the lower one of which {g) always grows without 

 further division into a long internode (frequently 5 to 6 cm. 

 in length) ; the upper one scarcely lengthens, but is first 

 divided in half by a vertical wall, and each half then 

 divides by further successive septa so as to form a whorl 

 of peripheral cells {b). From the node thus constituted 

 the leaves are developed, each from a peripheral cell, 

 and the normal lateral branches, which always originate 

 from the axil of the first or of the two first leaves of 

 the whorl. The leaves of such a whorl, from 4 to 10 

 in number, repeat in a modified manner the develop- 

 ment of the stem, but their apical growth is limited : 

 after the formation of a definite number of segments, 

 the apical cell ceases to divide and grows into the 

 terminal cell of the leaf which is usually pointed (Fig. 

 192,^, b"). From these leaves lateral leaflets may arise in 

 a similar manner to that in which the leaves themselves 

 have been formed from the stem ; and the leaflets may 

 again in turn produce others of a higher order. The 

 successive whorls of a stem alternate, and in such a 

 manner that the oldest leaves of the whorl, in the axils 

 of which the branches stand, are arranged on a spiral 

 line winding round the stem. Each internode also 

 usually undergoes a subsequent torsion in the same 

 direction. The lateral branches, of which in Chara one 

 is always developed in the axil of the oldest, in Nitella 

 one in the axil of each of the two oldest leaves of the 

 whorl, repeat the primary stem in all respects (Fig. 

 203). It has already been mentioned that the leaves 

 undergo a segmentation similar to that of the stem; they 

 also consist at first of very short internodes which are 

 afterwards greatly elongated (Fig. 192, 5, -y), and are 

 separated by inconspicuoi^ transverse plates or nodes. 

 From these the leaflets arise in whorls the members of 

 which are formed in succession, but they are directly 

 superposed one above another, and do not alternate 

 like the whorls of primary leaves (Fig. 193, C-E, /3). 

 (the basal node), by which it is united with the stem-node, and so is each leaflet 

 with its primary leaf. These basal nodes are the points of origin of the formation 

 of the cortex which, in the genus Chara, covers the internodes of the stem, but 



FIG. igi.— Chara /ra£-ilis ; sp germinat- 

 ing- spore; i d q pi together form the pro- 

 embryo (pi is segmented, which is not 

 clearly indicated in the drawing) ; at d are 

 the rhizoids iu ; iv' the so-called primary 

 root ; s the first leaves (not a whorl) of the 

 second generation or leaf-bearing plant 

 (after Pringsheim, X about 4). 



Each leaf begins with a node 



^ This has not yet been observed in Nitella. [See De Bary, Zur Keimungsgeschichte der 

 Charen, Bot. Zeitg, 1875. The carpospore is first divided by a wall at right angles to its long axis 

 into a small upper and a large lower cell. The upper cell is then divided by a wall at right angles 

 to the first into two equal cells : from one of these the pro-embryo is developed, from the other the 

 • primary root.'] 



