THE DICOTYLEDONES 



1707 



droops so that the flowers hang downwards and the tip of the perianth 

 closes over the mouth of the tube. 



It is interesting to note the analogy between the condition in this 

 family and in the entirely unrelated Araceae (see p. 2017). In the case of 

 the Wild Arum, Arum maculatum, the hairs protect an inflorescence, while 

 in this case they protect only a single flower. 



Included in the Rafflesiaceae are some of the most remarkable of the 

 parasitic flowering plants which, as a result of their mode of living, have lost 

 all resemblance to a normal Angiosperm (Fig. 1575)- The vegetative organs 

 consist of a cellular tissue resembling a fungal mycelium which ramifies 



Fig. 1575. — Distribution of Rafflesiaceae. The area should now be extended to include 



North Island, New Zealand. 



through the cambium region of the root, or occasionally the stem of the 

 host plant. In the tissues of the host the flower buds develop by a local 

 growth of the parasite tissue, until they ultimately burst out and appear 

 at the surface. These flowers may be solitary, as in Rajflesia, or they may 

 form an inflorescence as in Cytinus. The flowers are dioecious and vary 

 enormously in size, the largest being R. arnoldi (Fig. 1576) in Sumatra, 

 whose flowers measure a yard across. These flowers have a dull red 

 perianth composed of five segments which are liberally spotted with yellow 

 and surround a thick central ring (Figs. 1577 and 1578). In the centre of 

 the male flower is an upright column which terminates just below the ring. 

 This column is fringed by an indefinite number of anthers. The female 

 flowers produce a large number of carpels, each containing a number of 

 irregularly shaped cavities lined with small ovules (Fig. 1578). In Cytinus 

 the ovules are borne on branched parietal placentae (Fig. 1579). The 



