THE BOOT. 



75 



In SelagineB'a the roots are normally adventitious in 

 origin, arising laterally from the rhizophore (a stem- 

 structure) near its tip. In some shoots of 8. grandis 

 sent by Mr. Compton, of Cambridge, which had grown 

 in abnormally moist conditions, the rhizophores were 

 excessively (i. e. a few millimetres) short, bright green 

 and glabrous ; the single adventitious root was from 

 half an inch to an inch long, covered with dense white 

 hairs, and arose terminally on, and as a direct con- 

 tinuation of, the rhizophore ; the terminal position and 

 exogenous mode of origin are due to the precociousness 

 and exceptionally strong development of the root. 

 Bruchmann describes similar very short rhizophores as 

 a normal feature in the seedling. In the abnormal 

 shoots their constant position at the base of a stem-fork 

 shows them to be rhizophores and not roots; moreover, 

 in this genus roots are never normally formed di- 

 rectly on the stem. 



Adventitious roots may be induced to form freely 

 by artificially mutilating the stem. The method of 

 propagation of plants by means of cuttings rests on 

 this root-forming faculty of the stem ; in the case of 

 many plants the mere placing of the cut end of a stem 

 in water or moist air or soil is sufficient to cause 

 root-formation from the callus formed by the cambium; 

 as a rule, such roots are more readily formed from the 

 nodal'than from the internodal region. 



If the tips of the rhizophores of Selaginella (which 

 the writer has recently demonstrated to be morpholo- 

 gically of shoot-nature) be cut off, new roots can be 

 induced to form out of the callus at the apex. It is a 

 very interesting fact that if young pieces of the leafy 

 shoots of Selaginella be cut off and placed in sand, roots 

 can be induced to form directly from the base of such 

 a cutting. Groebel and Bruchmann both describe and 

 figure such cases (PI. V, fig. 5). 



Goebel figures a tuber of Corydalis solida which, on 

 being cut in two, developed roots from the lower cut 

 surface of the upper half. 



