60 PLANT PHYSIOLOGY 



sence of alcohol may be recognized by smell. According to DUDE (1903), 

 however, all plants which usually live under conditions of access to air do not 

 remain normal for long under those of intra-molecular respiration. Hence the 

 large amounts of alcohol which LECHARTIER and BREFELD (1876) obtained 

 from fruits and seeds after being for months deprived of oxygen doubtless did 

 not arise from intra-molecular respiration, but were due to the action of 

 lower organisms which had settled on them (comp. Lecture XVII). PALLADIN 

 (1904) also finds that in the case of green plants the amount of C0 2 given off 

 in a space free of oxygen rapidly decreases if micro-organisms are excluded. 

 Specially interesting is PETRACHEWSKY'S (1904) statement that the respiratory 

 coefficient of the alga Chlorothecium may rise to three times its normal value 

 when its respiration changes from intra-molecular to the normal type, and 

 then, after a short time, once more reaches its normal amount. LESCHTSCH 

 (1904) has shown the same phenomenon to take place in Saccharomyces (see 

 below). 



It is well known that alcohol and carbon-dioxide are not the only products 

 of intra-molecular respiration ; there are also higher alcohols, acids, aromatic 

 compounds, and hydrogen. "Whether these appear constantly we do not 

 know. Naturally the products will alter according to the respiratory material ; 

 hydrogen, for example, appears when mannite is abundantly provided. 

 Different substances, again, are unsuitable for intra-molecular respiration. 

 The results obtained by DIAKONOW (1886) were previously held to support 

 this view, viz. that intra-molecular respiration in general only took place in 

 presence of carbohydrates. More recently, however, KOSTYTCHEW (1904) has 

 definitely proved that it occurred (in Fungi) when quinic acid, tartaric acid, 

 and peptone were exclusively present, but it is not known whether carbo- 

 hydrates are not first of all formed from these bodies. At all events, intra- 

 molecular respiration goes on more readily and certainly in presence of sugar. 

 GODLEWSKI (1904) has shown that in seedlings proteid splitting in absence of 

 oxygen is carried out in a different manner than in its presence. There is none 

 of that accumulation of asparagin, &c., which we have already recognized as 

 due to secondary alteration of products of hydrolytic splitting. 



We may now turn to the problem of the factors concerned in respiration 

 (comp. BARNES, 1905). Respiration has been described as a combustion, 

 and this, no doubt, it is, if we regard only the end-products to which it gives 

 rise. If, however, we consider the chemical process itself we find it to be very 

 different from ordinary oxidation, at least if we regard combustion as a direct 

 union of oxygen and some other body. Sugar, starch, and fat, the substances 

 which disappear in the cell during respiration, do not combine with oxygen 

 at the low temperatures at which life goes on ; at least the formation of carbon- 

 dioxide from them has never been observed under the sole influence of oxygen. 

 Other reasons may be advanced, however, against the comparison of the com- 

 bustion of sugar in the organism with that of coal in a furnace, especially this 

 one, viz. that the amount of respiration is in great measure independent both 

 of the amount of oxygen and of the amount of respiratory material present. 

 Further, we have seen that the combustion is often by no means complete, 

 and is not carried out to the end-products H 2 and CO 2 , but stops at a definite 

 intermediate product, although oxygen is still available in sufficient quantity 

 to further oxidize these bodies. The best key to the real cause of respiration 

 is to be found in the phenomenon of intra-molecular respiration. We may 

 regard this as a new process which replaces normal respiration when oxygen 

 is deficient, or with PFEFFER we may look upon the two processes as funda- 

 mentally the same. This second conception is supported by most of the more 

 recent researches on the subject. In the first place, a splitting of organic 

 materials must occur, which goes on whether oxygen be present or not, and 



