304 



THALLOPHFTES, 



springs from the basal node of each leaflet. (Compare with this Fig. 197, yl and B.) In 

 reference to the origin of the carpogonium, A. Braun says (/.c. p. 69) that just as a branch 

 springs from the basal node of a leaf, so does the carpogonium from that of a leaflet (in 

 Cbara fragilis from the basal node of an antheridium which stands in the place of a 

 leaflet). As in the leaf which subtends a branch the ascending cortical lobes are wanting, 

 so also in the leaflet which bears the carpogonium the cells forming the ascending 

 portion of the cortex are also wanting. As it is the first leaf of the whorl on the stem 

 that produces a branch in its axis, so it is also from the first (inner) leaflet of the whorl 

 on the leaf that the carpogonium originates. The basal node of the antheridium in 

 C. fragilis has, according to A. Braun, not four peripheral cells, as in sterile leaflets, but 

 five ; an upper odd one which is first formed, two lateral ones which follow, and two 

 lower ones which are formed last of all. Of these five cells only the two lower ones are 

 developed into cells which form the cortex (of the leaves), the upper one, wanting in the 

 sterile basal nodes, is the mother-cell of the carpogonium ; but the two lateral ones 

 are developed into leaflets which stand laterally between the antheridium and carpogo- 

 nium {cf. Fig. 197, jS") ; these latter Braun calls Bracteoles. The mother-cell of the 

 carpogonium now grows out of the axil of the antheridium, and divides itself by a 

 septum into an upper outer terminal cell and a segment which in its turn is broken 

 up into two discs by a wall parallel to the previous one (Fig. 203, A, SK). The 

 lower cell does not divide any further, it forms the concealed pedicel of the car- 

 pogonium, and corresponds to the first internode of a branch ; but the upper one has 

 the character of a nodal cell ; it is divided by tangential walls into a zone of five outer 

 and one inner cell [SK') ; the former are the rudiments of the enveloping tubes, which 

 are therefore morphologically leaves. 



The Gharaceae are distinguished by the size of their cells, and by the simple relations 

 of the individual cells to the structure of the whole body. All the young cells contain 

 nuclei, which at first always lie in the centre of the protoplasm that fills the whole cell ; 

 each bipartition of a cell is preceded by that of the nucleus and the formation of two 

 new nuclei. As the cells grow, vacuoles form in the protoplasm which finally coalesce 

 into a single large vacuole (the sap-cavity). The protoplasm, now clothing the wall as 

 a thick layer, commences its rotatory motion which always follows the longest direc- 

 tion of the cell. Chlorophyll-granules are now formed : with the growth of the whole 

 cell they also grow and multiply by repeated bipartition; they adhere to the inner 

 side of the outermost thin stationary layer of protoplasm, and take no part in the 

 rotation of the layers which lie further inwards ; the nucleus, which is elongated and 

 granular, also lies in this layer \ The rotating protoplasm becomes differentiated, as 

 the ceil grows, into a portion which is very watery and others which are denser, 

 the former looks like hyaline cell-sap in which the latter float in the form of roundish 

 larger or smaller lumps. Since these denser masses are passively swept along by the 

 rotating clear protoplasm, as may be seen from their tumbling over one another, 

 the appearance is presented as if the cell-sap caused the rotating motion. Together 

 with the denser masses of protoplasm of less regular form, there are also a number of 

 bodies of globular shape covered with delicate spines, consisting also of protoplasm. 

 The current, as Nageli has shown, is most rapid next the stationary parietal layer, and 

 becomes gradually slower towards the interior; hence the spheres and globules which 

 swim in the thin rotating protoplasm tumble over one another, because they become 

 immersed at different spots in layers of different rapidity. Dependent on the direction 

 of the current, the chlorophyll-granules are arranged in longitudinal rows on the stationary 

 layer, and are deposited so thickly that they form a stratum ; they are absent only at the 

 neutral lines (Fig. 198, J, i). These neutral lines mark the position where the ascending 



* [In old internodal cells there are numerous nuclei which have been produced from the primary 

 nucleus by division and ' fragmenlation.' See Schmitz, Sitzber. d. niederrhein. Ges. in Bonn, 1879; 

 Unters. ueb. die Zellkerne der Thallophytcn. Strasburger, loc. cit. Johow, Bot. Ztitg. 1881.] 



