Chap, hi The Study of the Cryptogams 227 



Special researches on the anatomy of the Algae extended 

 over all the principal groups. The commensalism of Nostoc 

 and similar forms with other plants was investigated by 

 Janczewski and by Leitgeb in the case of Anthoceros, and by 

 Reinke in that of Gunner a in 1872. Klebs described other 

 instances of the same phenomenon in 1883. Bornet and 

 Flahault wrote on Nostoc in 1887, and Gomont investigated 

 Oscillaria in 1893. The question of the constitution of the 

 so-called nucleus in the Cyanophyceae was discussed by 

 Zacharias and by Wager in 1890 and succeeding years, and 

 its structure was determined in several cases. 



The Diatomaceae were described very fully by Prltzer 

 in Schenk's Handbuch of 1882. The formation of auxo- 

 spores and chlamydospores in the group was investigated 

 by Schmitz in 1877 and in 1884. Other researches were 

 those of O. Muller in 1883 and of Deby and Kitton a year 

 earlier. 



An important work on the reproductive processes of the 

 brown seaweeds was Berthold's Die geschlechtliche Fort- 

 pflanzung der eigentlichen Phaeosporeen of 1881. 



Towards the end of the century several of the problems of 

 the fecundation of the Phaeophyceae were solved. Farmer 

 and Williams were successful in observing the details of the 

 fusion of the spermatozoid and ovum of Fucus ; Williams 

 followed out the growth and development of Dictyota and 

 Taonia in 1897, though many of the cytological features 

 did not appear till after 1900. Janczewski traced the mode 

 of growth of the thallus of several members of the group 

 in 1895. Of more purely anatomical research, mention 

 must be made of the discovery of sieve tubes in the larger 

 species by Parker in 1881, Wille in 1885, and Oliver in 

 1887. 



Among the researches on the Chlorophyceae may be 

 mentioned the work on Cham of Pringsheim in 1864 and 

 of De Bary ten years later. Pringsheim discovered the 



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