418 BOTANY PABT n 



of the oogonium mother cell and are separated by delicate cell walls. The eggs 

 are enclosed within a thin membrane when ejected from the oogonium. This 

 membranous envelope deliquesces at one end and, turning partly inside out, 

 sets free the eggs (Fig. 360, 4, 5). The spermatozoids then gather round the eggs 

 in such numbers that by the energy of their movements they often set them 

 in rotation (Fig. 360, 6). After an egg has been fertilised by the entrance of one 

 of the spermatozoids it becomes invested with a cell wall, attaches itself to the 

 substratum, and gives rise by division to a new plant. 



In the case of other Fucaceae which produce four, two, or even only one egg 'in 

 their oogonia, the nucleus of each oogonium, according to OLTMANNS, nevertheless 

 first divides into eight daughter nuclei, of which, however, only the proper 

 number give rise to eggs capable of undergoing fertilisation. The other reduced 

 eggs, incapable of fertilisation, degenerate. 



Since the Fucaceae have no asexual spore-formation the alternation of genera- 

 tions characteristic of Dictyota is wanting in them. The thallus of Fncus, 

 developed from the fertilised ovum, has diploid nuclei. Reduction takes place in 

 the first two divisions within the oogonium and antheridium, so that four haploid 

 nuclei result. In the oogonium one further division, and in the antheridium four 

 take place before the sexual cells are produced. Thus in Fucus, in contrast to 

 Dictyota, only a very short haploid stage can be recognised. 



Economic Uses. The dried stalks of Laminaria digitata and L. Cloustoni were 

 used as dilating agents in surgery. IODINE is obtained from the ash (varec, kelp) 

 of various Laminariaceae and Fucaceae, and formerly soda was similarly obtained. 

 Many Laminarias are rich in MANNITE (e.g. Laminaria saccharina), and are used in 

 its production, and also as an article of food by the Chinese and Japanese. 



CLASS XI 

 Charaeeae (Stoneworts) ( 1( n > 48 ) 



The Charaeeae or Charophyta form a group of highly organised green Thallo- 

 phytes sharply isolated from both simpler and higher forms. Their origin must 

 be looked for in the Chlorophyceae, but the complicated structure of their sexual 

 organs does not allow of any immediate connection with the oogamous Green Algae. 

 On the other hand, in certain characters they show some approach to the Brown 

 Algae, from which they differ in the pure green colour of the chromatophores. 

 They cannot be regarded as leading towards the Bryophyta although their karyo- 

 kinetic nuclear division exhibits a great agreement with that of the Archegoniatae. 



The Charaeeae grow in fresh or brackish water, attached to the 

 bottom and covering extended areas with a mass of vegetation. Their 

 regular construction and habit is characteristic. In some species 

 the cylindrical main axes are over a foot in length, and are composed 

 of long internodes alternating with short nodes, from which short 

 cylindrical branches are given off in regular whorls with a similar 

 structure, but of limited growth (Fig. 361). The lateral axes are 

 either unbranched or give rise at their nodes to verticillate outgrowths 

 of a second order. From the axil of one of the side branches of each 

 whorl a lateral axis resembling the main axis is produced. The attach- 

 ment to the substratum is effected by means of colourless branched 

 rhizoids springing from the nodes at the base of the axes. The rhizoids 



