2oi8 A TEXTBOOK OF THEORETICAL BOTANY 



way out they crawl about over the maturing female flowers which, if they 

 have previously visited another flower, they will pollinate in the course of 

 their efforts to escape. As the female flowers mature the lower group of 

 hairs shrivels and the flies can now crawl further up the spadix. Here 

 they come into contact with male flowers whose anthers are just ripening. 

 The upper hairs are still turgid and prevent the flies from escaping and in 

 their struggles to do so they become covered with pollen from the male 

 flowers. Finally, after all the pollen has been discharged, the top cluster of 

 hairs also shrivels and the flies escape. Apparently the flies are unharmed 

 by their temporary imprisonment for often they immediately seek out 

 another spathe and repeat the process, transferring the pollen that covers 

 them to the female flowers as soon as they reach the bottom of the spadix, 

 and the process begins all over again. 



The genus contains twelve species which are distributed in central 

 Europe and the Mediterranean. Other interesting genera in this sub- 

 family are Dracuncidus, with two Mediterranean species, and Arisaema, with 

 about 105 species in Asia, Africa and North America. The flowers of this 

 genus are worthy of note. Extra-floral nectaries occur in the angles of the 

 leaf segments and in addition appendages are developed at the ends of the 

 leaf segments which resemble the end of the spathe. Insects creep easily in 

 the direction of the appendages to the nectaries, while others, possibly 

 misled by the similarity of structure, reach the spadix by creeping over the 

 spathe. Eventually they may find their way into the basal part of the spathe 

 and there effect pollination. Some species are said to be pollinated by 

 snails. 



The Pistioideae contain the single species P. stratiotes (Water Cabbage) 

 which is widely distributed in tropical and subtropical countries. It is a 

 floating water-plant, rarely anchored by its roots and often blown about by 

 the wind. The plant consists of a large rosette of leaves which remain 

 closed at night but open into a horizontal position by day. Stolons grow 

 out from the leaf axils which give rise vegetatively to new plants. The 

 inflorescence is small and monoecious, consisting of a whorl of male flowers 

 above and female flowers below. The male flower has two stamens, the 

 female an ovary produced from a single carpel. There is no perianth. It is 

 generally considered that this plant is a connecting link between the 

 Araceae and the Lemnaceae. 



TYPHALES 



The Typhales are aquatic or marsh-loving Monocotyledons which 

 develop extensive rhizomes. The leaves are linear, sheathing at the base. 

 The flowers are unisexual, very minute and crowded into clusters or dense 

 spikes. The perianth is either absent or reduced to scales. There are two 

 or more stamens and a unilocular ovary with a single pendulous ovule. 



According to Engler the two families Typhaceae and Sparganiaceae 

 should be united with the Pandanaceae and regarded as the simplest of the 



