ALGAE. CH ARACEAE, 



57 



longitudinal wall into two halves. By successive longitudinal divisions, which start 

 from the front wall and advance towards the hinder side, two interior cells and a 

 ring of from six to eight peripheral cells are formed. The oldest of these is also the 

 largest, for it grows more rapidly than the rest : it is the mother-cell and at the same 

 time the first apical cell of the new Chara, the leafy plant with sexual organs. The other 

 cells of the periphery may become the leaves at the angle where pro-embryo and 

 Chara-plant join, which are usually only rudimentary; these are the small leaves 

 surrounding the terminal bud of the stem which are shown in Fig. 34. 



From the nodes forming rhizoids are also produced accessory pro-embryos, and in 

 Chara aspera and others small white tubers formed chiefly by enlargement of the 

 lower segment of a lateral rhizoid ; when the tubers germinate they develope accessory 

 pro-embryos. 



The antheridia and oogonia are always formed on the leaves ; the antheridium 

 is the metamorphosed terminal cell of a leaf or lateral leaflet ; the oogonium in the 



FIG. 35. Chara fragilis. A middle portion of a leaf* with an antheridium a and an oogonium .9; c its crown ; 

 /3 a sterile lateral leaflet ; 8' larger lateral leaflets beside the fruit ; " the bracteoles springing from the basal node 

 of the sexual organs {rnagn. about 50 times), ff a young antheridium a with still younger oogonium 3k ; -w the 

 nodal cell of the leaf; u the point of union between this cell and the basal node of the antheridium ; /lumen of the 

 leaf-internode ; br cortical cells of the leaf. Magn. 350 times. 



monoecious species arises close beside it from the basal node of the leaflet in Chara, 

 cr from the last node of the primary ray which is crowned by a terminal antheridium 

 in Nitellaj the oogonium therefore is beneath the antheridium in the monoecious 

 species of Nitella, above or beside it in Chara. This relation of proximity disappears 

 in the dioecious species, but the morphological significance and position remain the 

 same. We will examine both organs first in their mature state. 



The antheridia (globules) are spherical bodies, from one half to one millimetre in 

 diameter, at first green, afterwards red. The wall is formed of eight flat cells, four of 

 which surround the free pole and are triangular, while the four at the opposite pole are 

 four-angled and a little narrowed below. Each of these cells is a definite portion ot 

 the wall of the antheridium and is called a shield ; in the unripe state their inner wall 

 is covered with green chlorophyll-corpuscles, which turn red as the antheridium matures ; 



