278 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



the form of the fruit. Especially is this true with ' Williams' Bon 

 Chretien,' and ' Beurr^ Bosc' Certain varieties show practically no 

 difference in size and* shape of fruit regardless of the pollen used, but 

 ' Howell ' and ' Winter Nelis ' are not of this class ; some varieties are 

 injured by this process. Thus ' Beurre Bosc ' should not be crossed with 

 ' Williams' Bon Chretien,' as the fruit so crossed is apt to be small and 

 misshapen, but when crossed with ' Doyenne du Cornice ' it is large and 

 fine. Concerning the best combinations of pears to plant, when ' Wil- 

 liams' Bon Chretien ' and ' Beurre d'Anjou ' are planted together they 

 both fruit well, also ' Winter Nelis ' and ' Doyenne du Comice ' make a 

 splendid combination. The pollen of any variety suits ' Howell ' and 

 ' Beurre Bosc,' but not every variety suits * W'illiams' Bon Chretien.' 

 It is suggested that in planting a pear orchard the best plan would be to 

 set from four to six rows in the following order: 'Williams' Bon 

 Chretien,' 'Beurre d'Anjou,' ' W^inter Nelis,' ' Beurr6 Bosc,' and 

 ' Howell.'— C. H. H. 



Potato Plant in Ireland, A Bacterial Disease of the. By Dr. 



G. H. Pethybridge and P. A. Murphy {Proc. Roy. Irish Acad. 

 xxix. (1911) B. 1, February 6, 1911; plates). — After a review of the 

 history of the bacterial diseases of the potato, the authors describe the 

 disease which is similar to "black-leg," under the ■ better name of 

 " black stalk-rot." The disease appears early in the season and plants 

 affected are characterized by the lighter colour of their foliage which is 

 occasionally spotted, and exhibits some amount of "leaf-roll." The 

 underground part of the stem is wholly or partly decayed, leaving only 

 the vascular bundles, or if partly decayed the tissues appear black. The 

 parent ' set ' is wholly decayed only the stalk remaining. In cutting 

 diseased stalks tranversely they will be found to be tough and their 

 bundles discoloured. The diseased tissues teem with bacteria. 



Attempts to isolate the organism have been successful, and its cul- 

 tural characteristics have been studied and are described. It is a rod- 

 shaped bacterium 1*3 /u to 1*8 fj, X 0*9 forming chains, and motile 

 having one to five peritrichous flagella. It liquefies gelatin forming 

 greyish colonies, and growing well on most culture media. 



When inoculated into the tuber (as it may be naturally) a cavity is 

 produced containing a light brown pulp generally marked off from the 

 healthy tissue by a distinct black line. The organism may pass into the 

 vascular bundles which then become dark, but occasionally the pulp 

 remains almost pure white. The pulp is at fii'st amphoteric in reaction 

 but the acidity is more strongly marked than the alkalinity. On expo- 

 sure to air, however, it becomes markedly alkaline. 



The organism is nearly allied to Bacillus phytoplithorus and the 

 authors suggest the name B. melanogenes for it. 



The disease is probably contracted in the soil, but the planting of 

 affected sets is mainly responsible for the spread of the disease. Con- 

 siderable loss is sustained in the growing crop, but more in the stored 

 potatos. All affected plants should be destroyed, diseased tubers should 



