SUPPLEMENT 59 



It is not easy to say whether proteid or other nitrogenous organic sub- 

 stances are employed as respiratory materials by the higher plants ; it is, 

 however, very probable that the changes which we saw taking place in the 

 mixture arising from proteid hydrolysis when the seedlings were kept in the 

 dark are due to oxidizing processes. Indeed, it has been suggested by BERTEL 

 (1902) and CZAPEK (1906) that tyrosin becomes oxidized very generally in the 

 plant into homogentisinic acid, nevertheless the observations of SCHULZE and 

 CASTORO (1906) go to prove that there is no homogentisinic acid in the plants 

 CZAPEK experimented with. Hence, it is impossible to make any definite 

 statements at present as to the oxidation products of tyrosin. However it may 

 be, one thing is certain, that the higher plant differs in one respect very greatly 

 from the animal, viz. in that it does not excrete the decomposition products 

 of its nitrogenous compounds, but uses them once more in constructive meta- 

 bolism ; it is able to re-employ as nutrients both the nitrogenous and non- 

 nitrogenous end-products of metabolism. Since animals have no such power, 

 they are dependent on plants to provide them with carbohydrate and proteid. 



The question whether proteid may be used for respiratory purposes is 

 not so easy to answer ; we will confine ourselves to the question whether any 

 of it must be used for that purpose. We shall return to this point again at the 

 end of this lecture, after we have considered the dependence of respiration on 

 external conditions. 



201, 11. 11-13, f or Since in other . . . MAXIMOW read The question cannot be 

 considered as in any way settled, for MAXIMOW 



I. 22, for vital processes. The plant must be read vital processes ; in other 

 words, the plant is 



II. 23-42, for If, however . . . beetroot read Other authors, e.g. ZIEGENBEIN 

 (1893), KUNSTMAN (1895), STOKLASA (1903), demonstrated for respiration a 

 typical optimal curve. The question has, doubtless, on the other hand, lost 

 greatly in interest because in assimilation and respiration we must regard the 

 part of the curve where the ascent is less, or where even a fall takes place, as 

 under all conditions due to injury (BLACKMAN, 1905). The difference between 

 respiration and assimilation would consist in the fact that in the former this 

 injury first occurs at temperatures which paralyse every faculty in the plant, 

 while assimilation is already retarded at lower temperatures. 



11- 53~5 f or Respiration . . . during drought read Respiration ceases 

 entirely in perfectly dry parts of plants, and seeds, mosses, lichens, and the 

 like, which can tolerate desiccation, may remain alive during drought 



202, 1. 2, after (KoLKWixz, 1901) read It appears not improbable that the 

 diminution in respiration observed by LEWIN (1905) in seeds under pressure 

 is only the result of a more limited water content. 



1. 16, after poisons read (e.g. formaldehyde and the salts of certain metals) 



1. 18, after 1899 read ; ZALENSKI, 1902 



1. 21, after RICHARDS, 1896 read ; SMIRNOFF, 1903 ; KRASNOSSELSKI, 1905). 

 That materials which in small quantities act as stimulants should inhibit 

 in greater concentrations goes without saying. 



1. 28, for in which . . . reduced read compressed 



1. 55, for When glucose read If glucose, 



203, 1. i, after and insert should ; for becomes read become 

 1.2, for remains read would remain 



1. 7 P. 204, 1. 4 from bottom, for Thus BREFELD . . . RACIBORSKI (1905) 

 read One can arrange for the absence of oxygen, essential to intra-molecular 

 respiration, by allowing seeds to soak under water. Thus, if large seeds of 

 Vicia Faba, after being kept under water for two days, be crushed the pre- 



