64 FIRST GROUP.— THALLOPHYTES. 



between the antheridium and oogonium (Fig. 35, A, B") ; these are called by Braun 

 bracteoles. The mother-cell of the oogonium grows out of the axil of the antheridial twig 

 and divides by a transverse wall into an upper, outer, apical cell and into a segment, 

 which divides in its turn by a wall parallel to the first into two discs [sk in Fig. 41, A) ; 

 the lower cell does not divide, but forms the concealed pedicel of the oogonium and 

 answers to the first internode of a branch ; the upper cell is of the nature of a nodal cell 

 and divides by tangential walls into a circle of five outer and one inner cell [s M) ; the 

 former are the rudiments of the tubes which form the envelope, and whose origin agrees 

 with that of the leaves. 



A remarkable case of parthenogenesis has been observed by De Bary in Chara 

 crinita '. Male plants of this dioecious species are extremely rare, and are known only 

 in a few herbarium specimens. The oogonia are formed in the same way as in other 

 Charas, and have the five fissures in the neck before fertilisation. Oospores were 

 produced in abundance on female plants which were cultivated by themselves, and on 

 which there was no trace of an antheridium ; scarcely one proved abortive, notwith- 

 standing the entire absence of fertilisation. Oospores thus produced germinated in the 

 usual manner. 



The Characeae are distinguished by the size of their cells and by the simplicity 

 of the relations of the single cells to the structure of the whole. The young cells 

 have a nucleus, which always lies in the centre of the protoplasm fiUing the cell, 

 and divides, as usual, previously to the division of the cell. In the internodal cells, 

 which do not divide but elongate, Schmitz ^ has observed a peculiar fragmentation 

 of the nucleus into anumber of daughter-nuclei. The nuclei in the nodal cells suffer no 

 further change. As the cell increases in size vacuoles are formed in the protoplasm 

 which at first fills the cell completely, and these vacuoles ultimately become confluent 

 and form a single large vacuole, the sap-cavity. The protoplasm, which covers the wall 

 of the cell as a thick layer, now begins its rotating movement, choosing always the 

 longest path in the cell. The chlorophyll-corpuscles, which now make their appearance, 

 grow with the growth of the cell and multip'y by repeated bipartition ; they adhere to 

 the inner surface of the outermost thin motionless layer of protoplasm, and take no part 

 in the rotation of the layers which lie further inside. With increase of growth in the 

 cell the rotating protoplasm is differentiated into a watery and a less watery denser 

 portion, the former having the appearance of hyaline cell-sap, in which the latter floats 

 in the form of roundish lumps of varying size ; and as these denser masses are passively 

 carried along by the rotating hyaline protoplasm, as can be seen by their tumbling over 

 one another, the appearance is as though the movement of rotation was in the cell-sap 

 Along with the lumps of denser protoplasm of more irregular form are many spherical 

 protoplasmic bodies, which are covered with fine rod-like projections and are known as 

 ciliated bodies (' Wimperkorperchen'j. The movement is, as Nageli shows, most 

 rapid next the motionless wall-layer, and grows gradually slower towards the inside ; 

 hence the round masses floating in the thin rotating protoplasm tumble over one another, 

 because they impinge with different portions of their surface on layers having different 

 rates of speed. The chlorophyll-corpuscles are arranged according to the direction of 

 the current in longitudinal rows along the layer of motionless protoplasm, and are often 

 so thickly crowded together as to form a continuous stratum. They are absent only at 

 the so-called /lei/iral zones (Fig. 36, /). These mark the line where the ascending and 

 descending portions of the rotating protoplasm of a cell flow alongside of one another in 

 opposite directions, and where therefore there is rest. The direction of the movement 

 of rotation in each cell stands in regular relation to that in all the other cells of the 

 plant, and therefore to its morphological structure, as Braun has shown. 



' See also Braun, Ueber Parthenogenesis Lei Pflanzen (Abh. d. Berl. Akad. 1856, p. 337). 



2 Schmitz in Sitzungsber. d. niederrh. Ges. 4 Aug. 1879, p. 25 of the reprint.— Strasburger, 

 Zellbildung. u. Zelltheilung, III. Aufl. p 228.— Johow, Die Zellkerne von Chara foetida (Bot. Zeit. 

 1 88 1, p. 729). 



