202 CLIMBERS, PARASITES, SAPROPHYTES. 



[234. Cultivated Climbers. The following twiners are often 

 cultivated : Scarlet Runner, Dutchman's Pipe (Aristolochia), 

 Jasmine, Wistaria, Morning Glory (Ipomoea), "Tea-plant" 

 (Lycium), and various species of Convolvulus, Honeysuckle, etc. 



Cultivated tendril-bearers show many points of interest. Some have 

 ordinary coiling tendrils, which may be branches, e.g. Passion-flower, 

 Trumpet-flower (Bignonia}, Vine, various species of Virginian 

 Creeper (Ampdopsis) ; or modified leaflets, e.g. Sweet Pea, Garden 

 Pea; or whole leaves, e.g. Cucumber, Vegetable Marrow; or 

 prolonged leaf -tips, e.g. Mutisia (Compositae), Gloriosa (Liliaceae) ; or 

 sensitive leaf -stalks, e.g. Clematis, Solanum jasminoides, Maurandia, 

 Tropaeolum, Nepenthes; or modified stipules, e.g. Smilax ; or coiling 

 roots, e.g. Vanilla Orchid. The tendrils of Self-clinging Virgi- 

 nian Creeper (Ampelopsis veitchii) differ from those of other Virginian 

 Creepers in being branched, each branch ending in a sticky disc, so 

 that this plant can climb up walls. In Cobcea scandens, a greenhouse 

 climber, the tendrils are branched and each branch ends in a hook ; 

 the tendril is very sensitive, and the hooks enable it to hold on to a 

 support until it has had time to coil round it. 



Among root-climbers, which send out negatively heliotropic 

 attaching roots like those of Ivy, are the following cultivated 

 climbers: Rooting Trumpet-flower (Tecoma radicans, allied to 

 Bignonia), Poison Ivy (Rhus toxicodendron, rather like a Virginian 

 Creeper, but leaf with three leaflets only, and their margin is entire or 

 nearly so), and the Climbing Pig (Ficus repens, with small leaves ; 

 the climbing-roots secrete sticky juice, and as this dries the root-tip is 

 firmly cemented to the support). These root-climbers can, like Ivy, 

 climb up walls.] 



235. Parasites and Saprophytes. In our work on the 

 nutrition of plants, we have so far dealt only with the manu- 

 facture of food by photosynthesis, the raw materials being 

 water, dissolved earth- salts, and atmospheric carbon dioxide, 

 the energy required for the process being derived from sun- 

 light by means of chlorophyll. Some plants obtain their food 

 in a totally different way, by living as parasites on other 

 living plants (or on living animals in the case of some bac- 

 teria), or as saprophytes on dead organic matter. 



Parasites and saprophytes are distinguished as total or 

 partial, according to whether they get the whole, or part only, 

 of their food in these ways. Plants which have no chlorophyll 

 are necessarily total parasites or saprophytes, since they can- 

 not use free carbon dioxide, and must obtain carbon in the 

 form of organic compounds. Fungi and bacteria can usually 

 obtain the nitrogenous part of their food from fairly simple 

 nitrogen compounds e.g. salts of ammonia and some of 



