114 



BOTANY 



In Caulerpa (Fig. 87) the plant resembles closely one of the higher 

 land-plants, showing a creeping stem which produces roots from its 

 lower side and leaflike branches from its upper surface. There 

 is, however, no trace of cellular structure, the thick wall of the 



tubular thallus being supported 

 by numerous threadlike braces, 

 which traverse its interior. 



In most of the large forms, 

 like Codium (Fig. 85, B), Hali- 

 meda, and others, the thallus 

 is composed of extensively 

 branched, but nonseptate fila- 

 ments, whose extremities are 

 often composed of club-shaped, 

 closely set branches which 

 form a sort of cortex, or rind, 

 upon the outside, while in the 

 central part the filaments are 

 much more slender and loosely 

 interwoven. 



Reproduction. Non-sexual repro- 

 duction may be brought about by 

 the separation of a portion of the 

 thallus, this being the only form of 

 reproduction known in Caulerpa. 

 More commonly swarm-spores are 

 produced, and in some instances apla- 

 nospores. 



In Botrydium the whole proto- 

 plasmic contents of the plant may 

 break up into swarm-spores, but in 

 the higher forms a portion of the 

 plant is shut off as a sporangium. 

 The zoospores in Botrydium have 

 but a single cilium, or flagellum 

 (Fig. 84, B), but in most Siphonese 

 there are two. The very large zoo- 

 spores of Vaucheria (Fig. 88, D) 

 have many cilia, but examination 

 shows that these are in pairs, corresponding to the nuclei which are distributed 

 in the colorless superficial layer of protoplasm. In this case the giant zoospore 

 is to be considered as a compound structure made up of many biciliate zoo- 

 spores. The zoospores germinate at once. 



Sexual Reproduction. In Caulerpa no trace of sexual reproduction has been 

 discovered, and our knowledge of many other marine forms is still incomplete. 

 In Botrydium very small gametes are produced from aplanospores, which form 

 in great numbers at the end of the growing period. These become red in color, 

 and sometimes form a brick-red film upon the ground where the plants have been 

 growing. They germinate quickly, after a proper period of rest, and the con- 



FIG. 86. a, Halimeda monilis (x|); 6, 

 longitudinal section, highly magnified. 

 (After MURRAY.) 



