THE DICOTYLEDONES 



1881 



Fig. 1 79 1. — Getitiana campestris. Field Gentian. lona. 



alpine situations, while a few occur as halophytes. The Asiatic genus 

 Crawfurdia is a climber. Certain genera live as saprophytes. They are 

 found chiefly among the American species, though the condition is also 

 known among certain Asiatic and African forms. In these cases the plants 

 are small herbs in which the leaves are reduced to scales. Menxanthes 

 trifoliata (Fig. 1792), the Bog Bean, has alternate leaves and this genus 

 together with Limnantheniiim (Fig. 1793) is sometimes separated into a 

 distinct family. They are aquatic or marsh plants, and large idioblasts are 

 developed in the floating leaves. Anatomically they are also separated by 

 the vascular bundles, which in Gentiana are bicollateral, while in Menxanthes 

 they are simply collateral. The flowers are adapted to insect pollination, and 

 are usually brightly coloured. The fruit is a capsule, containing many 

 minute seeds. A mycorrhizal fungus appears to be present, at least in many 

 species, and is suspected of assisting germination. Recent experiments on 

 vernalization of the seeds have proved particularly successful, for the 

 germination of Gentiana seed is notoriously difficult. 



The Apocynaceae are a rather larger family with about 1,000 species 

 distributed among 130 genera. They are mostly found in the tropics but a 



