30 PLANT PHYSIOLOGY 



between chlorophyll and haemoglobin on which BAYER based his hypothesis 

 cannot be maintained nowadays ; but one may easily get over the difficulty 

 of assuming a development of carbon-monoxide which in itself suggests many 

 criticisms if we start, not as we have been doing from the anhydride CO 2 , but 

 from carbonic acid itself (H 2 C0 3 ). 



113, 1. 6, after H 2 CO 3 read or partly in the dissociated condition HC0 3 



11. 16-37, f or Many arguments ... be correct, read Should formaldehyde 

 arise in this or in some other way (comp. CZAPEK, Biochemie, I. 503) its con- 

 densation to a sugar, outside the plant at least, presents no special difficulty. 

 BUTTLEROW (1861) and LOEW (1886) successfully accomplished such a con- 

 densation by simple methods, and obtained formose a mixture of sugars 

 with the fundamental formula C 6 H, 2 O,.. That a similar condensation, however, 

 takes place in the plant may be regarded even now as open to doubt. In the 

 first place, it is by no means certain whether formaldehyde is demonstrable 

 in the plant, although it has often been so asserted (PoLLACCi, 1902 ; GRAFE, 

 1906 ; USHER and PRIESTLEY, 1906). That there are other aldehydes present 

 has been established by CURTIUS and REINKE (1897), but these doubtless 

 have nothing to do with carbon-dioxide assimilation. Still the absence of 

 formaldehyde is no serious argument against the hypothesis, for if it really 

 be an intermediate product in carbon assimilation it would naturally be at once 

 transformed, and hence would never accumulate in any quantity. Such an 

 accumulation would, indeed, be injurious, since formaldehyde is a virulent 

 poison. This leads us to another objection made to BAYER'S hypothesis. It 

 has been clearly shown that formaldehyde in a concentration of I in 20,000 

 or even I in 50,000 is seriously inimical to green cells (BOKORNY, 1897), but 

 TREBOUX (1903) has shown that a solution of i in 200,000 is not injurious to 

 Elodea, so that one must admit that it may occur in chloroplasts if it be rapidly 

 transformed. A third, and perhaps the principal, objection raised is that it 

 has not been found possible to induce a formation of starch, either in light or 

 darkness, by supplying formaldehyde to chloroplasts (TREBOUX, 1903), although 

 this must certainly occur if the hypothesis be correct. 



I. 45, for p. 341 read p. 326 



II. 46-9, delete Experiments ... in the light. 



114, 11. 16-43, for In the first place ... in that form, read In the first place, 

 we know that every part of the plant suffers considerable loss of organic sub- 

 stance owing to respiration acting in the reverse way to carbon-dioxide assimila- 

 tion (Lecture XVI), and, further, owing to the continuous withdrawal into the 

 stem of considerable quantities of soluble carbohydrate (Lecture XIV). 



We cannot refer here to the way in which SACHS established a measure 

 for the amount of this loss, but merely give the results he obtained, which 

 were, that Helianthus formed 1-7-1-88 g. and Cucurbita 1-5 g. of dry weight 

 per hour per sq. m. Taking these numbers as a basis, SACHS reckoned that 

 a vigorous active sunflower can manufacture 36 g. and a cucumber 185 g. of 

 dry weight in the course of a warm and bright summer day. I\^ore recently 

 ARNO MULLER (1904) has carried out estimations as to the amount of assimila- 

 tion in various leaves, using the same method, and has arrived at the following 

 results : 



Carbohydrate formed per hour and per sq. m. in gr. 



Amyliferous leaves : Nymphaea Rumex Petasites Helianthus Nicotiana 



2-373 2-215 2-045 1-823 1-378 



Sacchariferous leaves : Tulipa Arum Colchicum Allium 



1-267 1-004 1-217 I-I93 



The value given above for Helianthus agrees exactly with that obtained 



