Chap. III. INJURING THE PEIMAEY EADICLE. 189 



wards produce lateral and horizontal branches; and 

 they then present a curious appearance, as if a young 

 fir-tree had grown out of a ball of clay surrounding 

 the branch. These upright shoots have manifestly 

 changed their nature and become apogeotropic ; for if 

 they had not been affected by the ^cidium, they 

 would have grown out horizontally like all the other 

 twigs on the same branches. This change can hardly 

 be due to an increased flow of sap into the part ; but 

 the presence of the mycelium will have greatly dis- 

 turbed its naturar constitution. 



According to Mr. Meehan,* the stems of three 

 species of Euphorbia and of Portiilaca oleracea are 

 " normally prostrate or procumbent ;" but when they 

 are attacked by an -^cidium, they " assume an erect 

 habit." Dr. Stahl informs us that he knows of several 

 analogous- cases ; and these seem to be closely related 

 to that of the Abies. The rhizomes oi Sparganium 

 ramosum grow out horizontally in the soil to a con- 

 siderable length, or are diageotropic ; but F. Elfving 

 found that when they were cultivated in water 

 their tips turned upwards, and they became apogeo- 

 tropic. Tlie same result followed when the stem of the 

 plant was bent until it cracked or was merely much 

 bowed.t 



No explanation has hitherto been attempted of such 

 cases as the foregoing, — namely, of secondary radiclss 

 growing vertically downwards, and of lateral shoots 

 growing vertically upwards, after the amputation of 



* 'Proc. Acid. Nat. Sc. Phila- viously observed ('Flora,' 1878, 



delphia,' June 16th, 1874, and p. 324) that the underground 



July 23rdj 1875. shoots of Triticum repena bend 



t See F. Elfving's interesting vertically up when the parts above 



paper in 'Arbeiten Bot. Institut., ground are removed, and wljen 



in Wiirzburg,' vol. ii. 1880, p. 489. the rhizomes are kept partly im 



Carl Kraus (Triesdorf).had pre- mersed in water. 



