TYPES OF CRYPTOGAMS; THALLOPHYTES 



255 



302. Other Florideae. Nemalion represents one of the simplest 

 modes of fruiting in the red algae. In others there is great variety in 

 structure and great complication in the mode of fruiting. Some 

 species of Polysiphonia (or Dasya) may well be studied in compari- 

 son with Nemalion and in further illustration of this important 

 group. 1 Understanding that a siphon, in algae, is a row of cells, end 

 to end, study the structure of a plant of Poly- 

 siphonia as illustrating its name. How many 



siphons are there ? Do the main branches 

 have any other cells covering the surface (cor- 

 ticating cells) ? 



Note the tufts of repeatedly forking, one- 

 siphoned filaments. 



303. Fruiting of Polysiphonia. The anther- 

 idia are to be sought on the branching fila- 

 ments just mentioned. Note how they differ 

 from those of Nemalion. The clustered fruits 

 or cystocarps will be recognized as ovoid- 

 globose or urn-shaped bodies attached 

 externally to the frond. Note whether 

 the group of spores is naked or otherwise, @ 

 whether the spores are produced singly 



or in chains ; how attached ; shape. 



Many Floridece have another kind of 

 fruiting bodies, spores produced without 

 fertilization, coordinate with the asexual 

 spores of black mould (see Sect. 308). 

 In Florideae, such spores are usually 

 found in fours and are called tetraspores. 



Are tetraspores usually found on separate plants ? 



In Polysiphonia the tetraspores appear to be formed in threes 

 (tripartite}, the fourth being underneath the three. When found, 

 describe their position and arrangement. 



304. Algae. Diatom, Oscillatoria, Pleurococcus, 8pi- 

 rogyra, Vaucheria, Nitella, Fucus, Nemalion, these eight 



1 It is desirable also to exhibit fresh or pressed specimens of various genera 

 to show their general aspect. 



FIG. 188. 



A, spores of Nemalion (greatly 

 magnified); , portion of 

 thallus of a red alga, Lejo- 

 Hsia, with tetraspores, t. 



