DEVELOPMENT AND REPRODUCTION 293 



workers succeeded in inducing the development of lactiferous glands in virgin 

 females of the rabbit by injecting an extract of the foetus from a pregnant female. 

 The artificially produced gland was about as large as in the case of a normal 

 pregnant female at about the ninth or tenth day of pregnancy. 



The following quotation from Biedl^ gives an idea of some modern concep- 

 tions concerning hormone action. "Today we find that the theory of internal 

 secretion plays an important part in nearly all the problems of physiology and 

 pathology and that it is very important in connection with general biological 

 problems. Nothing is more characteristic of the recent change in our attitude 

 toward the r6le of specific internal secretions than is Schiefferdecker's hypothesis 

 concerning the r61e of specific internal secretions in the control of the nervous 

 system. This hjrpothesis supposes that the influence upon other cells, exerted 

 by the metabolic products emanating from nerve cells during their ordinary 

 nutritive processes, is tropistic in nature, while the influence exerted by sub- 

 stances arising in nerve ceUs during their special activity is to be considered as a 

 stimulating one. These conceptions of the nature of nervous control are now 

 indeed, generally accepted, but they show very clearly how our attitude toward 

 nerve activity has changed in recent times. All correlations in activity between 

 organs used to be regarded as nervous phenomena, now nervous control is 

 regarded as of a chemical nature." 



Hormones probably occur also in plants, as well as in animals.^ Even as 

 early a writer as Duhamel gave vague expression to the idea that various phe- 

 nomena of plant growth and development are not to be explained by reference to 

 external conditions alone, and Sachs elaborated this idea and expressed the 

 opinion that an explanation of many such phenomena must be sought inside the 

 plant itself. In a paper on the relation of material to the form and structure 

 of plant organs' this author expressed himself very definitely, stating that 

 "with a diversity in the form of organs goes a corresponding diversity in the 

 materials of which they are composed." Before Brown-Sequard and other 

 authors entered this field in animal physiology Sachs had written of organ- 

 forming materials {"Organhildende Stofe"), and in his work concerning the 

 influence of ultra-violet rays upon the formation of flowers he wrote: "These 

 flower-forming substances act, like ferments, upon large masses of plastic 

 material, although they themselves are present in exceedingly small amounts."* 

 If the word hormones is substituted for ferments in this sentence the statement 

 becomes quite modern. Many phenomena of growth and of the developmental 

 configuration of plants will surely be found to be dependent upon various hor- 

 mones, and one of the main problems of future investigators will doubtless deal 

 with these internal secretions of plants. 



» Biedl, Arthur, Innere Sekretion. Ihre physiologische Gmndlagen und ihre Bedeutung fur die Patho- 

 logie. Berlin, 1910. P. 23- 



2 Massait, Jean, Essai de classification des reflexes non nerveux. Ann. Inst. Pasteur is : 635-672. 

 1901. [Idem, same title. Receuil Inst. Bot Bruxelles s; 299-34S. 1901.I 



' Sachs, J. von, StoS und Form der Pflanzenorgane. Arbeit. Bot. Inst. Wurzburg 2 : 452-488, 689-718. 



1882. 



• Sachs, Julius, Ueber die Wirkung der ultravioletten Strahlen auf die Bluthenbildung. Arbeit. Bot. 

 Inst. Wurzburg 3 : 372-388. 1887. Idem, Gesammelte Abhandlungen iiber Pflanzenphysiologie i : 307- 

 309. Leipzig, 1892.* 



