THALLOPHYTA— ALGiE 63 



and branches, and consequently divided into nodes and inter- 

 nodes. The branches are developed in the axils of the leaves. 

 The lower portion of the stem gives rise to a number of adven- 

 titious roots, which are filamentous and multicellular. 



The growth of root, stem and leaf is apical ; in the stem 

 and branches it is carried on by an apical cell. 



The nodes and internodes differ in structure ; in the latter 

 the central core is formed by a single very elongated cell, 

 which in the older parts contains several nuclei. It is not a 

 coenocyte, the nuclei being derived from the fragmentation of 

 the original nucleus. This cell is covered in by a cortex 

 consisting of a number of rows of cells which spring from the 

 nodes above and below and accompany the internodal cell in 

 its elongation. The nodes are made up of a number of small 

 cells, from the external ones of which the branches and leaves 

 arise. 



The growing point of the stem of Chara is seen in fig. 810. 

 When it divides it cuts off a segment by a transverse wall ; 

 this cell is again divided similarly into two, of which the upper 

 becomes a nodal and the lower an internodal cell. The nodal 

 cell divides by vertical walls, while the internodal one only 

 elongates. The peripheral one& grow upwards and downwards 

 to help to form the cortex of the internode above and below 

 it. The apical cell of the leaf is similar to that of the stem, 

 but it only keeps its activity for a short time. The apical cell 

 of the root is not differentiated. 



The reproductive organs are antheridia and oogonia, and 

 are produced at the nodes of the stem. The antheridiim is a 

 shortly- stalked globular body, sometimes called a globule. Its 

 case consists of eight cells with curious thickenings upon their 

 surfaces. The top cell of the stalk projects into the interior 

 of the antheridium between the bases of the lower cells of the 

 case. Each of the eight wall-cells, known as shields, bears a 

 long cell projecting into the interior, which is termed a manu- 

 brium ; this is crowned bj' a smaller globular cell, the cajn- 

 tulum,, and this in turn gives rise to six secoiidary capitula. 

 Springing from each of these are two long filaments, divided 

 into a large number of cells, each of which gives rise to a single 

 antherozoid. The antherozoids are twisted masses of proto- 

 plasm, bearing two cilia at their anterior ends. 



The oogonium is also stalked, the central cell being sur- 

 rounded by filaments which arising beneath it from the node 

 coil spirally romid it. Each filament cuts off a small cell at its 



