i82 LIFE : OUTLINES OF GENERAL BIOLOGY 



minute glands (liydathodcs). which probably get rid of surplus water 

 and keep a sap-current agoing, for an above-ground fohage is 

 represented only by soaks on the purplish upright flower-stalk. As 

 there is no chlorophyll the organic food is entirely obtained, as in 

 the broom-ra|x\ from the roots of the host-plant. This is another of 

 the cases in which the steeds will not germinate unless they are 

 brought into contact with the roots of the appropriate host. 



In those tropical countries in which conditions favour vegetative 

 e.xuberance. there is, partly because of the lu.xuriance, a frequent 

 overcrowding and an inttnse comixtition. Hence also the frequency 

 of particular adaptations such as climbing and such as root-parasit- 

 ism. The latter tinds abundant illustration in the family Balano- 

 phoreic. often gorgeous in flower colouring, and large in size though 

 with reduced foliage. The only luiropean representative is 

 Cvno9nonum coccineum, which is found in southern countries as a 

 root -parasite on Pistacia and nnTtle. In this family the union of 

 parasite and host is marked by tulxilike swellings in which the 

 tissues of the two plants come into very intimate union. 



In another family, that of the KafHesias, the parasitism goes ev^n 

 further, for the tropical species have lost not only leaves and chloro- 

 phyll, but tlie roots and the stem itself. From the seedling there 

 develops a hollow fibrous cylinder which embraces the stem and 

 r(K)t of the host— often a vine — and gives origin to an internal web 

 of ab.sf)rbing filaments. In some cases, e.g. Pilostyles, these suctorial 

 threads suggest the hyph^e of a fungus, and, as Neger aptly says, 

 the parasite has sunk, as regards its vegetative system, from the 

 level of an ordinary flowering plant to that of a Thallophyte! But 

 the flowering system suffers no degeneration. F>om the hidden 

 filaments there grow flower-buds which burst through the host's 

 bark or root-corte.x and develoj) extraordinarily. In a famous species, 

 Rafficsia arnoUii, the flower is blood-red in colour, with a carrion 

 stench, and a diameter of about a yard— easily the largest of known 

 l)looms. The only Furo]xan re])res«ntativc of the order of Rafflcsias 

 is the Mediterranean Cyiinus hypocisiis, whose puzzling flower-buds 

 burst through the ground from the roots of a shrubby rock-rose 

 (Cistus). and develoji into "a flowering spike of scarlet scales and 

 yellow flowers". 



It is interesting to notice that dodders, broom-rapes, Balano- 

 phoras and Rafflesias belong to different orders of flowering plants; 

 for this shows how the same way of living and somewhat similar 

 adaptations may evolve indejxndently from different origins. 



We have ke]>t by themselves the jvirtial root-parasites, such as 

 cyebrights (Euphrasia), yellow rattles (Rhinanthus), and cow-wheats 

 (.Melampyrum). which r»>tain their chloro])hyll and their leaves, 

 but have their roots intimately fastened to those of grasses and 

 herbs, from which they absorb elaborated food. Many plants which 



