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Evolutionary changes of masses and periods under the influence of gravitational radiation (GR) are computed for binaries with main-sequence or degenerate hydrogen-helium (H), helium (He) and carbon (C) secondaries. Tracks in the P-M2 and P-M2 planes are determined. The orbital period of systems P with a non-degenerate dwarf filling its Roche lobe decreases until the time-scale of GR (-10 9 -10 1°y rs) becomes shorter than the thermal time-scale T^ of the mass losing component M2. When M2 becomes ~0.1 M Q , JP begins to increase. This could account for the existence of the minimal P ~ 1.3" and for the accumulation of observed cataclysmic binaries (CB) below P < 2. The GR can be the driving force for evolu tion of cataclysmic binaries: TT Ari, OY Car, Z Cha, and WZ Sge as their P^ M2 and M2 indicate. The rate of mass exchange driven by GR is ~ 10 9 -10 10 M 0 /yrs. It is enough to feed the X-ray bursters and related objects.

With 1 3 1;igures. (Received 1971 3lay 2 0 )Difficulties of the niixing length theory when applied to convective envelopes oI Iliain sequencc stars, rcd giants and white dwarfs are discussed. It is shown that not only the value of the mixing length, b u t also other parameters of the theory influence strongly the obtained solution. l h e necessity of improvement of the theory is stressed.Die Schwieriglteitcn der Theorie des >lischungswcgcs in bezug auf die lionvektiven au0ercn Schichten von Hauptreihensternen, rotcn Kicscn und wei0cn Zwergen werden behanrlelt. Es wird gezeigt, daU nicht iiur die GrADe des Mischungsweges, sondern auch die anderen Parameter der Theorie des Niischungswegcs cinen groRen EinfluR auf das Ergebnis der Hechnungen ausuben. Die Notwendigkeit eincr Verbesserung der 'lheoric wird unterstrichen.

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