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SCIENCE. 



[N. S. Vol. V. No. 113. 



ment and to those interested in the theoretical 

 questions of reproduction, but it is one which 

 ■will be a great aid to teachers who wish to 

 supply material of these lower forms of algae to 

 tTieir classes in a condition in which these pro- 

 cesses of reproduction can be observed. This 

 is especially so in the case of certain species 

 of VaucJieria, Hydrodidyon, Oedogonium and 

 others, since the conditions have been deter- 

 mined under which one can with certainty bring 

 the material to the production of zoospores, or 

 to the development of sexual organs within a 

 reasonable limit of time. 



His most extended experiments were con- 

 ducted upon species of Vaucheria, especially 

 upon Vaiicheria repens, clavata and sessilis, or 

 upon the composite species Vaiicheria sessilis, as 

 some would treat it. Klebs would, however, 

 treat these three forms as species, and it is in- 

 teresting to see how the reactions of these tliree 

 forms toward various conditions of environment 

 and artificial treatment give support to the 

 view that they may be regarded as species, and 

 we are promised a thorough-going revision of 

 the species of Vaiicheria from the hand of one 

 of Dr. Klebs' students. 



The experiments cannot be given in detail, 

 but under the head of the asexual reproduction 

 through zoospores the methods employed were 

 similar to those noted in 1892. Plants culti- 

 vated in the light and in moist atmosphere, 

 on being transferred to water produce numer- 

 ous zoospores; cultivated in a 0.2 per cent, 

 to 0.5 per cent, nutrient solution (inorganic 

 salts) in the light, on being transferred to pure 

 water produce zoospores. On the other hand, 

 cultures in water, or in a 0.1 per cent, to 

 0.2 per cent, nutrient solution, produce zoo- 

 spores on simply being darkened. The devel- 

 opment is especially active when the first or 

 second method is combined with the third. In 

 studying the conditions which influence sexual 

 reproduction he found Vaiicheria repens the best 

 subject, though any of the species studied could 

 be brought with certainty in artificial cultures 

 to form sexual organs. For example, threads of 

 Vaucheria repens placed in a 0.2 per cent, to 0.4 

 per cent, cane-sugar solution form sexual organs 

 with the greatest certainty in four to five days. 

 In studying the influence of light he found that 



it acts in a two-fold manner. Through the as- 

 similation of CO2 reserve material, in the form 

 of organic compounds, which is necessary for 

 sexual reproduction, is supplied, and the light 

 also acts in a direct way stimulating the pro- 

 cess. This was proved by growing cultures 

 under conditions where an abundance of light 

 was supplied, but the plants were deprived of 

 the CO2 of the air, so that none or little carbon 

 assimilation took place and no sexual organs 

 were formed. Cultures, under similar con- 

 ditions, in a cane-sugar solution, produced sex- 

 ual organs, the reserve material here being 

 supplied by the sugar solution. On the other 

 hand, cultures in a cane-sugar solution in weak 

 light or in darkness produced no sexual organs. 

 The same results were obtained in cultures of 

 other genera of algre, and his conclusions that 

 light acts in a twofold manner seem justified. 



In studying the conditions which influence 

 the male or female organs some interesting re- 

 sults were obtained, though no definite conclu- 

 sions were reached regarding the relation be- 

 tween these two kinds of organs. Cultures in 

 a thermostat at 25° to 26° C. showed a ten- 

 dency to complete suppression of the oogonium 

 or to a vegetative growth of the same, the 

 number of oogonia in a group being not in- 

 cresed, while the antheridia were increased in 

 number in some cases as much as five- to seven- 

 fold. Cultures under air pressure of 120 mm. 

 gave similar results. 



In his studies of Drapernaudia glomerata he 

 discovered microzoospores and observed their 

 conjugation to form Zigospores. Pringsheim, 

 in 1860, first observed resting cells, and speaks 

 of the formation of microzoospores, though he 

 does not describe them. Klebs first observed 

 them in 1894. Algse were taken from a cold 

 standing culture and placed in a 2 per cent, 

 cane-sugar solution in the heated laboratory'. 

 After twenty-four hours zoospores were formed, 

 and after forty-eight hours microzoospores ap- 

 peared. The microzoospores are oval to spher- 

 ical and about half the size of the zoospores, 

 and are four ciliate. The red-eye spot is near 

 the base of the body while in the zoospores it 

 is situated at the upper third. Many of the 

 microzoospores form resting spores partheuo- 

 genetically, though, as stated above, Klebs was 



