698 BOTANY part ii 



Differences are, however, found within the order. In Areca catcelfu, the fruit 

 developed from a similar ovary to that of Cocos is a berry, the exocarp becoming 

 partly fibrous and partly succulent. The white endosperm is here of stony 

 consistence, cellulose being stored as a reserve material ; the endosperm is 

 ruminated, i.e. the dark seed-coat grows into it at many points and gives it a 

 veined appearance. The fruit of the Date Palm (Phoenix dactylifera) is also a 

 berry, but this arises from one of the carpels of the apocarpus gynaeceum, the 

 other two not developing. In contrast to the other genera mentioned, Phoenix 

 is dioecious. Other important economic plants among the Palms are Elac'is 

 guineensis, the African Oil Palm, species of Calamus which yield Malacca Cane, 

 and species of Metroicylon, from which Sago is obtained ; the two latter are found 

 in the Asiatic- Australian region of the tropics. Phytelephas onacrocarpa, an 

 American Palm which does not form a trunk, yields vegetable ivory (the hard 

 endosperm). Several species yield a flow of sugary sap on cutting off the 

 inflorescence, and this is sometimes fermented to make Palm-wine and sometimes 

 used as a source of cane-sugar (Arenga saccharifcra). 



Family 5. Araeeae. — The Araceae are mostly herbs or shrubs ; 

 they take a conspicuous place as root-climbers in the damp tropical 

 forests. The leaves of some species {e.g. Monstera) have the large 

 lamina incised or perforated ; this comes about by the death of 

 definitely limited areas and is comparable to the method by which 

 the leaves of Palms become compound. Flowers are greatly reduced, 

 usually diclinous, borne on a swollen, fleshy axis ; a spathe, often of 

 bright colour and serving to render the inflorescence conspicuous, 

 is present at the base of the spike {e.g. Anthurmvi scherzemmum, 

 Richardia aetJiiopica, both of which are commonly cultivated). Fruit 

 usually a berry. 



Acorus calamus has, in the course of the last two or three centuries, spread to 

 this country from the East. It has complete, hermaphrodite flowers (^^) ; ovary tri- 

 locular. The short spadix is terminal, but is disjilaced to one side by the spathe 

 which resembles the foliage leaves (Fig. 759). 



Poisonous. — Many Araceae are poisonous. Calla palustris in peaty swamps. 

 Arum maculatum (Fig. 760), a perennial herb with tuberous rhizome, common in 

 woods. It develops a number of stalked, hastate leaves, the brown spots on which 

 give the plant its specific name. The flowers are monoecious, without perianth ; 

 the female flowers stand at the base of the spadix and the male a short distance 

 above them. Above the latter come a number of sterile flowers with downwardly 

 directed, hair-like points, which stand at the level of the constricted portion of the 

 spathe ; this is widely ojjen above. These hairs allow insects, attracted by the 

 peculiar scent or seeking warmth (cf. p. 248), to creep into the lower expanded 

 portion of the spathe, but prevent their return until the female flowers have been 

 pollinated from another individual. Wlien this is accomplished the hairs wither 

 and the anthers open. The escaping insects, now dusted with pollen, may enter 

 other inflorescences and pollinate the flowers. 



Family 6. Lemnaceae. — The Duck-weeds of our ponds and streams have naked 

 monoecious flowers liorne in depressions of the body of the plant. The flowers are 

 surrounded by a small spathe. Lemna, Wolffia. 



