for peas, log. ( 1.345 - \y )= .1286 - .24.t; 



15 .— '■■ 



78 • PHYSIOLOGY [BoT. Absts., Vol. IX, 



GROWTH, DEVELOPMENT, REPRODUCTION 



516. Crocker, William. Conditions affecting flower development. [Rev. of: (1) Klebs, 

 George. Ueber die Blxitenbildung von Semperviviun. (Flov?er formation in Sempervivum.) 

 Flora 11-12: 128-151. 5 fig. 1918 (see Bot. Absts. 2, Entry 601); (2) Fischer, H. Zur Frage 

 der Kohlensaure-Ernahrung der Pfianzen. (Carbonic acid nutrition of plants.) Gartenflora 

 65: 232-237. 1916; (3) Kraus, E. J., and H. II. Kraybill. Vegetation and reproduction with 

 special reference to the tomato. Oregon Agric. Exp. Sta. Bull. 149. 90 p. 1918 (see Bot. 

 Absts. 1, Entry 1402).] Bot. Gaz. 67: 445-446. 1919. 



517. MiTSCHERLicH, E. A. Ein Beitrag zum Gesetze des Pflanzenwachstvuns. [The 

 law of plant-growth.] Fiihling's Landw. Zeitg. 68 : 130-133. 1919. — The author calls attention 

 to a general phenomenon of growth in organisms, viz., slow initial growth, a period of rapid 

 growth, and a period of slow growth as maturity sets in.^He reports determinations of dry 

 weight produced during the grand period of growth in cultures of peas and mustard. Deter- 

 minations were made at quasi-definite stages of growth; for example, the appearance of the 

 1st tendril-bearing leaves, and of 4th pair of leaves (in peas). The stages of growth did not 

 represent the same time interval in all cases. — Values closely approximating the observed 

 were given by the equations, 



for mustard, log. (1.26 — 'SJy |= .1— Ax', 

 in which y = the average dry weight of plants at the .rth growth period. — H. S. Reed, 



518. MiTSCHERLicH, E. A. Zum Gesetze des Pflanzenwachstimis. [The laws of plant 

 growth.] Fiihling's Landw. Zeitg. 68: 419-426. 1919.— This is a rejoinder to Rippel's discus- 

 sion and criticisms (see Bot. Absts. 9, Entry 519). — The rate of growth of organisms is 

 expressed by the differential equation, 



dy 



in which y = the mass of the plant at time x, A = the final (limiting) value of y, and c = a 

 constant. Various methods of integration give equations which express the value of y for 

 any positive value of x. Robertson's equation, 



\og-^^ = K{t-h), 

 A- X 



gives, for small values of x, values which are larger than the observed, while Mitscherlich's 



equation, 



/ n _ w _ \ 'I ,— 



log I ylA - yly )=log aIA - c.x, 



gives lower values. Somewhat better agreement may be obtained in the case of plant growth 

 if the weight of the seed planted be deducted. Rippels' theory that during the first stage 

 of growth there is some sort of a retarding factor is contradicted. The 2 equations are 

 examined for their ability to express the growth of gourd fruits, Vicia Faba roots, peas, 

 and mustard plants. — The somewhat polemical discussion concludes with the statement that 

 Rippel's criticisms in no way invalidate Mitscherlich's previous statements. — H. S. Reed. 



519. RiPPEL, A. Die Wachstumkurve der Pflanzen und ihre mathematische Behandlung 

 durch Robertson und Mitscherlich. [The growth curves of plants and their mathematical 

 treatment according to Robertson and Mitscherlich.] Fiihling's Landw. Zeitg. 68: 201-214, 

 1919. — This is a critical examination of the applicability of formulas proposed by Robertson 

 and by Mitscherlich (see Bot. Absts. 9, Entry 517, 518) to the growth of plants. It contains 

 citations to cognate studies, and deals with the rate of growth of root zones, of seedling 



