Scrophulariaceae. 495 



In those species in which the main root is vigorous 

 and branched, the development of adventitious roots is 

 repressed, and does not, at any rate, occur except in old 

 individuals (cf. Th. Resvoll, 1917, p. 215); in the species 

 of the other group adventitious roots are more or less abun- 

 dantly developed, certainly according to the nature of the 

 substratum. The length of the first vegetative-stage varies, 

 as a rule, it may be of several-years duration. The variations 

 must be assumed to be due to the varyingly favourable 

 conditions afforded by the habitat in question, as for in- 

 stance, early disappearance of snow in spring. 



In P. lanata the winter-buds are protected by the large 

 persistent bases of the fohage-leaves of the year's rosette; 

 in the other species special bud-scales occur. 



P. euphrasioides appears, perhaps exceptionally, to be 

 able to occur as a biennial hapaxanth. The growth of the 

 main shoot — in all the species which have been investigated 

 — terminales by the development of a floral portion, fre- 

 quently furnished with a few or several foliage-leaves, but 

 sometimes quite devoid of these (individuals of P. siidetica 

 and Sceptrum carolinum). The adventitious shoots arise most 

 frequently in the axils of the scale-leaves; previous to their 

 flowering they usually pass through a vegetative stage of 

 some years duration. Only in P. euphrasioides the shoots 

 usually appear to be able to achieve flowering in their second 

 year. After fruit-setting the upper part of the shoot dies 

 away; the complex of the persistent basal-portions forms a 

 rhizoma multiceps (a mesocorme), which is especially large 

 and vigorous when the main root is of long duration, as in 

 P. hirsiita and lanata; these species also form the largest tufts. 



In those species in which the main root and rhizome 

 die away quickly behind, and adventitious roots are abun- 

 dantly developed (especially in P. siidetica and Sceptrum caro- 



32* 



