THE LOKANTHACE^ OF CEYLON. 101 



This straij^litening of the hypocotyl occurs even wlien the seed, after its hypocotyl has 

 become fixed on the branch, is placed in the dark. 



Just before or just after the hypocotyl has straightened itself, the cotyledons, together 

 with the endosperm enclosing them, are shed and the minute plumule exposed for the 

 first time (fig. 6 e, PI. XI.) ; at other times the cotyledons come out of the endosperm 

 and remain for some time enclosing the plumule. 



At this stage the young plant is 2-3 cm. long, and dark green. Its sucker has 

 swollen to two or three times its original size (fig. Cyf, PI. XI.) — so much so as to suggest 

 that it acts as a tem])orary storehouse of material transferred from the endosperm, md 

 the cotyledons, before both these are, as just described, cut off. 



At this stage the sucker, although firmly adherent to the bark, has effected but little 

 penetration into the tissue of its host. 



Fig. 3. 



r'-^ r~^^-'"^f^-T ^ 



The first pair of leaves remain rudimentary and arc soon shed ; the plumule forms a 

 very short internode (1-2 mm.) from which another pair of minute deciduous leaves arise ; 

 later as many as four or five very short internodes may be formed (woodcut 3), each 

 bearino- small deciduous leaves, very rich in tannin. In most species shoot -differentia- 

 tion takes place very slowly, owing doubtless to the great task of penetrating the host 

 with which the entering " root " is confronted, a task of vital and immediate importance. 

 After penetration is effected, the growth becomes very rapid indeed; large leaves, 

 resemblin"" in shape those of the mature plant, arise, the internodes lengthen, and the 

 stem throws out branches. 



It often happens, however, especially when the branch on which the seed is fixed is 

 small or poorly nourished, that, before the large leaves arise, whilst the internodes are 

 very short, a lateral aerial root is thrown out from the sucker, and this root grows rapidly 

 along the branch — soon seeking the underside. In extreme cases, quite large suckers 

 may arise on this aerial root before the mature leaves are formed. 



I cannot but think that this early putting out of the aerial root is a phenomenon of 

 heredity, and throws light on the course by which the LoranthaceaB become parasites : 

 the seeds, originally sticky, often lodged on tree-, and, as in many species of Fie m, these 

 seeds, germinating, threw out roots which rapidly reached \\w i,-round or the earth which 

 collects in the forks of trees. To enable the plant to exist in this early non-parasitic 

 stage the base (free end) of the sucker came to function as a reserve food store. Prom this 

 stage the natural semi-parasitism was reached by the ability of certain cells of the distal 



p2 



