BOT.-VOL. II.] PEIRCE— ROOT-TUBERCLES. 32 1 



they enter. ^ The effect on the nuclei is marked, as will 

 be shown presently. 



The changes which take place in infected cells as they 

 develop are indicated in figs. 14 «, b, c, d. These repre- 

 sent successive cells from the meristem backward toward 

 the center of the tubercle, which is shown in fig. 7. A 

 part of the cambium layer at a-h in fig. 7 is shown at x-y 

 in fig. 14 a. This series is stained by Flemming's triple 

 stain, but Gramm's iodine was not used. For this reason 

 the bacteria and infection threads are not differentiated. 

 The magnification of figs. 14 b, c, d is 300, that of fig. 14 a 

 is 270, hence 14 b and 14 a do not meet exactly. The fig- 

 ures in the series had to be drawn separately by reason of 

 the limited field of the objective which was used to give the 

 necessary magnification. 



Two cells of the tubercle cambium are shown at x-y. 

 Recently formed daughter-cells lie toward the outside as 

 well as toward the center of the tubercle. The cell z is 

 already beginning to show the effects of infection, vacuoles 

 of considerable size, which later become confluent, form- 

 ing in the cytoplasm, and a distinct vacuole, like a halo, 

 appearing around the nucleolus. As shown by the cells 

 further toward the center of the tubercle, the nucleolus is 

 the first part of the nucleus to be evidently affected by the 

 presence of tubercle bacteria in the cell. It is the first part 

 of the cell to decrease in size and to disappear. If the 

 nucleolus is in fact an accumulation of food in the nucleus, 

 one would expect it to disappear, to be consumed, when- 

 ever there arose a special need of food in the nucleus, or 

 even in the cell as a whole perhaps. Furthermore, the 



1 W. Magnus (1900) discusses the endotrophic mycorrhiza fungus of Neottia nidus 

 avis Iv. in this connection, stating (pp. 7-9) that the hyphse of this fungus do not grow 

 toward the nucleus of the cell with any regularity, but that in many other parasitic 

 fungi the hyphse do grow toward and around the nucleus, in some cases, however, with 

 no greater regularity than toward aud around starch-grains or other solid contents of 

 the cell. He adds (p. 61): " Dass sich parasitare Pilze mit ihren Haustorien oft an den 

 Zellkern legen und sich in seiner Nahe eigenthiimlich verzweigen, gestattet keiuen 

 Ruckschluss auf die Bedeutung des Kernes als Nahrungscentrum der Zelle." To con- 

 clude, because fungus hyphee or strands of bacteria grow toward the nucleus of a cell 

 which they have entered, that the nucleus is the center of nutrition of the cell is 

 illogical; but it may well be in these cases that the nucleus contains or produces sub- 

 stances which nourish and attract the parasites. 



