240 BOTANICAL GAZETTE [September 



thread formed in the earliest stages of division merely serves as a path along- 

 which the nucleolus passes its chromatin/' The author has evidently over- 

 looked or failed io take into consideration the chromatin-nucleoli or karyo- 

 somes, which in well stained preparations of Vicia are always visible in the 

 resting nuclei. The fact that in some forms of mitosis the true nucleolus — 

 or plasmosome — is at the time of division entirely cast out of the nucleus 

 into the cytoplasm, where it degenerates, has not been taken into considera- 

 tion. That the nucleolus does contribute something to the chromatm is 

 probably true, but it is very doubtful if it plays such an important part as has 

 been assigned it by the author. The conclusion seems to be based largely 

 on the staining reactions of iron-haematoxylin and Bordeaux red. Most cytol- 

 ogists now place little reliance on staining reactions.— W, J. G, Land. 



A TURNIP ROT has been under study for some time by Professor M. C. 

 Potter of the Durham College of Science, England, and a number of articles 

 have been published concerning it. In a communication to the Royal Society 

 on June 12 the parasitic activity of the disease organism, Pseiidomonas 

 destructans, is minutely described. By direct observation it was seen to 

 swell the wall of a healthy cell to two and a half times its natural thickness 

 within an hour, by action of cytase which it excretes. The swelling could 

 be recognized almost at once upon the introduction of the germs. Almost 

 an hour, however, was required to make evident the toxic action by which 

 the protoplasm is killed, followed by contraction and separation from the 

 wall. The penetration of the cell wall by the bacteria was also directly 

 observed, the time required being about three hours. All stages of this 

 operation were well demonstrated by fixing, paraffin imbedding, and section- 

 ing. Differential staining, using ruthenium-red for the walls and Lowit s 

 method for the bacteria and their flagella, brought out the fact with great 

 clearness. The enzym secreted by the organism is incapable of acting upon 

 the mature and old epidermis. Entrance into the plant under field conditions 



appears to be largely through wouiids. Such an unequivocal demonstration 

 of a bacterial disease of plants is a notable addition to our knowledge 01 

 plant pathology, and is especially interesting as it comes from across the 

 Atlantic, where it has been, and is still, much the fashion among writers of 

 all classes to deny that bacteria are capable of originating disease in plants. 



J. C. Arthur. 



In a paper read before the Society for Plant Morphology and Physi- 

 ology, J. M. Macfarlane=4 gives an historical r^sum^ of the progress of 

 plant cytology. He classifies the problems of plant cytology as morpholog- 

 ical, physiological, experimental, ecological, evolutionary, and taxonomic. 

 He suggests that the nucleoplasm and general cytoplasm may be regarded 



'■^Current problems in plant cytology. Contrib. Bot. Lab. Univ. Fenn. 2: I^S" 

 204. //. /<?. igo2. 



