652 



algjE or hydeophyta. 



presence is said to give rise to malaria. Occasionally they communi- 

 cate their odour to the water of reservoirs, and render it unpleasant. 

 It is of importance for Water Companies to see that Charas do not 

 exist in the streams which supply the water for their reservoirs. 



Order 224. — Alg^, or Hydeophyta, the Seaweed Family. 

 Cellular plants, found both in salt and in fresh water. Fronds com- 

 posed of variously formed, often elongated, cells, which are either 

 simple or branched filaments, continuous or articulated, separate, or 

 combined in different ways (fig. 29), so as to constitute fronds of 

 various kinds (fig. 899). Growth takes place by the division of cells, 

 or by cellular prolongations, in the form of lateral branches. Eepro- 

 ductive organs consist of spores (figs. 467-470, p. 265), which are 

 contained in mother-cells or perispores (•^sf ', around, and avo^a, seed), 



Kg. 

 901. 



Fig. 899. 



Fig. 903. 



or sporocarps (xaj's-o's, fruit). These are sometimes congregated to- 

 gether in receptacles of different sorts (figs. 899 c c, 900). The 

 spores occasionally divide into 3 or 4 cells, constituting tetraspores 

 {riTgag, four), (fig. 482, p. 273). In addition to spores or sporocarps 

 (fig. 902 sp), there are antheridia, consisting of minute cells, with 

 spermatozoids in their interior. In some of the simplest Algae, the 

 whole plant is concerned in producing new individuals by division of 



Figs. 899-903. Frond and organs of reproduction of Fucus serratus, to illustrate the 

 natural order Algffi. Fig. 899. The entire plant much diminished in size. /, Frond com- 

 posed of cells, so united as to form a flat expansion, c c, Conceptacles at the extremities 

 of the frond, containing the organs of reproduction. Fig. 900. Extremity of the frond 

 covered with conceptacles. Fig. 901. Vertical section of a conceptaole, c, with its inner 

 surface covered with spores (sporocarps), paraphyses, and antheridia. t. The superficial 

 ceUular tissue of the frond, in which the conceptacle is buried, o. Foramen by which the 

 conceptaole opens externally. Fig, 902. Spore, sp, covered with its perispore or sporo- 

 carp, p. /, Filaments or paraphyses, by some called antheridia. Fig. 903. Spore, s, sepa- 

 rated and deprived of its perispore or outer covering. 



