NOTES AND ABSTEACTS. 871 



the tuber being made up of two swollen ends joined by a constricted part ; 

 in less marked cases the tubers are abnormally elongated. The author 

 ascribes this to " Durchwachsen," literally " through-growth," a kind of 

 proliferation. The through-growth is due to the parent tuber, after having 

 completed its normal growth, growing again at the crown end, with the 

 result that a new tuber is formed attached to the old one. At the same 

 time the plant may produce new tuber-bearing branches, of a later growth. 

 The result is that the crop from certain varieties consists of three kinds 

 of tubers, viz. mature, immature, and through-grown which are partly 

 mature and partly y.oung. The through-grown new crown end is 

 frequently produced at the expense of the heel-end, which becomes 

 shrivelled. The varieties under experiment were German ones, with 

 names unfamiliar in Britain. Early and middle-late varieties rarely 

 produce through-grown tubers, but some late varieties are liable to do so. 

 Mature tubers are richer in starch, and cook better than immature. 

 Through-grown tubers with shrunken basal ends are more watery and less 

 palatable than mature tubers. After keeping over winter, immature and 

 through-grown tubers showed a much higher percentage of rotten tubers 

 than was found when tubers stored were fully mature. Through-grown 

 tubers used as " seed " produce weaker plants. They are thus generally 

 defective, and the author recommends growers to avoid varieties which 

 produce many through-grown tubers. It is also an abnormality to be 

 avoided in selecting new varieties. — W. G. S. 



Potatos, Cork-formation on wounded. By Lauritz Olufsen 

 (Beih. Bot. Cent. xv. pp. 269-308 ; with four text figures). — An investiga- 

 tion into the manner in which wounds on Potatos are healed over. He 

 finds that unripe tubers react more quickly than usual to the stimulus of 

 the wound, whereas dead and thickened tissue parts are unable to transfer 

 the stimulus. The cells immediately below the ordinary skin show very 

 little sensitiveness. 



Cork-formation follows on all sorts of wounds. If the cork skin 

 only is removed, the place heals over by the continual action of the 

 cork cambium. If a pea-root enters a Potato, the wound becomes healed 

 in the ordinary way ; though corrosion of the starch occurs, no cellulose- 

 or starch-dissolving ferments are given off by the root. Lenticels may 

 appear under water and only become healed over under very dry conditions. 

 The cork cambium is produced deep below the surface over pith and 

 cortex, but close to the surface over the vascular bundle. The formation 

 of the wound cork is accompanied by the disappearance of starch in the 

 cells. The starch between the wound and the cork cambium is thus 

 saved to the plant. The wound cork is even better adapted to protect 

 against micro-organisms than the original skin. Light does not markedly 

 affect the healing process, but the presence of oxygen is a necessary factor. 

 The wound cork is best produced under moderately wet conditions, but is 

 not impossible under water. Transpiration is not proved to be the 

 exciting cause of cork formation. Poisonous solutions do not entirely 

 prevent cork formation, though mercury vapour, iodine, and ethylic ether 

 vapours are injurious, and may even prevent it in strong doses. 



G. F. S.-E. 



