78 PLANT PHYSIOLOGY 



place in KUHN'S experiments then neither alinite nor any other artificial nitro- 

 genous manure should be needed. Experience, however, teaches us the con- 

 trary ; as a rule, nitrogenous manuring is essential and Leguminosae only are 

 exceptional. The Leguminosae 



236, 1. n, for 0-21 read 0-021 



1. 32, for save . . . addition of read without added 



I. 35, for other . . . soils read to be quite unable to use other sources of 

 nitrogen than those present in soil, 



II. 39-40, for and an experiment . . . growth took place read when it was 

 found that many behaved in precisely the same way as cereals, for growth 

 took place 



237, 11. 7-9, for since the extract . . . fruiting stage read since the extract 

 of a sugar-beet soil, in which peas and various species of clover had been culti- 

 vated for a long time in regular rotation, 



1. 18, for ' To show read ' In order ; before make insert may 



I. 30, for FRANK (1890), read NOBBE and HILTNER (comp. LAFAR'S 

 Mykologie, II. 24) 



II. 32-55, for Without going into details . . . took place, read BEIJERINCK 

 (1888) having isolated the bacterium (B. radicicola} and cultivated it by itself 

 apart from the plant, PRAZMOWSKI (1890, 1891) succeeded in observing the 

 mode of infection of the leguminous root. He established the fact that the 

 Bacteria enter the root-hairs and, in the form of closed tubular masses, grow 

 through first the hair and then the neighbouring cortical cells (Fig. 42). When 

 these infection tubes have penetrated a certain depth into the root the Bacteria 

 escape from them and fill the cells of the root. Just as we shall see in the case 

 of gall insects, so the Bacteria exert a stimulus on the parenchymatous cells 

 affected, and induce in them vigorous growth and division. A local hypertrophy 

 is set up the nodule or bacterial gall (Fig. 43, a, b). In the central cells of this 

 gall the originally rod-shaped Bacteria swell and assume branched forms, rich 

 in proteid, which have been long described as ' bacteroids '. In all probability 

 these are degeneration forms, since they have also been observed in other 

 Bacteria and described as involution forms. Several authors have succeeded 

 in seeing the origin of these bacteroids in nutrient solutions apart from the plant 

 (BEIJERINCK, 1888 ; HILTNER, 1900 ; STUTZER, 1901). According to HILTNER 

 (LAFAR, III. 51) this result is easily obtained by providing a surplus of carbo- 

 hydrates or organic acids in the culture. Many authors have made attempts 

 to demonstrate a combination of nitrogen in pure cultures of B. radicicola. 

 Ammonia was generally presented to the bacterium to act as a source of nitrogen, 

 or no combined nitrogen at all was given in the hope that the combination of 

 free nitrogen might be in this way all the more easily observed. All attempts 

 of this kind were quite unsuccessful. 



238, 11. 8-19, for MAZE'S results . . . view to take, read More recently his 

 results have been called in question by HILTNER (LAFAR, III. 50), and so 

 we must regard the nature of the symbiosis between B. radicicola and Legu- 

 minosae as not yet entirely cleared up, for the whole problem is by no means 

 so simple as was previously supposed. It is not simply a case of the leguminous 

 plant supplying the carbohydrate and the bacterium the nitrogen, thus making 

 possible a mutually passive existence on the part of both organisms. HILTNER'S 

 observations, on the contrary (LAFAR, III. 45), point to a constant parasitism 

 of the bacterium, under certain conditions, or at least at first. How the host 

 is able to accommodate a parasite as what might be termed a commensal we do 

 not know ; nor do we know what the exact role of the bacteroids is. 



