296 PLANT SOCIOLOGY 



leptophylls up to 25 sq. mm.; nanophylls up to 225 sq. mm.; microphylls 

 up to 2,025 sq. mm.; mesophylls up to 18,225 sq. mm.; macrophylls up to 

 164,025 sq. mm.; and megaphylls larger than macrophylls (see Fuller and 

 Bakke, 1918). 



2. Macrophanerophyta (trees) : renewal buds He more than 2 m. aboveground. 

 Raunkiaer (1918) distinguishes three size classes, but since the climatic 

 difference between 30 cm. and 2 m. above the soil is much greater than 

 between 6, 16, or 25 m., it seems justifiable to combine them. As in the case 

 of the shrubs, a subclassification may be made. 



3. Phanerophyta succulenta (stem succulents) (Fig. 151): characterized by the 

 lack of leaves and fleshy, slightly lignified water-storage tissues. They are 

 excellently adapted to steppe and desert conditions and actually inhabit 

 chiefly the desert regions of the earth, reaching their culmination in the 

 Cactaceae of North and South America. Europe has only a few representa- 

 tives in the Mediterranean genus Caralluma and some introduced cacti. 

 In north Africa there are a few succulent Euphorliias such as E. resinifera, 

 E. beaumierana, E. echinus, and a few Compositae of the genus Kleinia. 

 Winkler (1910) distinguishes: 



a. Cactoid forms. 



h. Barrel-shaped stem^s (Bombaceae, Sterculiaceae). 



c. Fleshy stems {Sarcocaxdon, Pelargonixim). 



d. Massive succulents {Testudinaria, Adenia globosa, etc.). 



4. Phanerophyta herbaceae (herbaceous stems): characteristic of the moist, 

 warm, equatorial regions; with the size of trees or shrubs they combine 

 slightly lignified, herblike, and therefore tender aerial shoots, usually large 

 leaves, and naked buds. They seem to thrive especially well under the 

 protection of higher trees. This groxip includes species of Begonia, Euphor- 

 biaceae, Musa, Impatiens, Piper, etc. 



5. Phanerophyta scandentia (lianas): climbing plants whose renewal buds 

 pass the unfavorable season high above the ground. The annual leaf and 

 shoot climbers which die off every winter to the ground like Bryonia and 

 Humulus belong to the hemicryptophytes and therophytes. The true 

 lianas, woody plants which grow up to the light by the aid of various sup- 

 ports, are characteristic of the tropical virgin forest. They decrease in 

 number with distance from the equator. Only a few of them reach the cold- 

 temperate zone, such as Clematis, Hedera and Lonicera. 



X. EPiPHYTA ARBORicoLA (tree epiphytes): highly specialized independent 

 phanerophytes. They settle upon trunks and branches and live upon the food 

 substances collected between the clefts and angles of the bark. Like the lianas, 

 the higher epiphytes reach their fullest development in the humid tropical forest. 

 In the tropical forest of Barro Colorado Island the epiphytes and lianas constitute 

 respectively 10.4 and 15.7 per cent of all vascular plants, and hemiepiphytes are 

 frequent (Kenoyer, 1929). In the temperate zone they are represented only by 

 the woody hemiparasites {Viscum, Loranthus) and by the so called occasional 

 epiphytes. A number of ecological subdivisions may be distinguished. Besides 

 the semiparasitic epiphytes referred to above, there are: stem-tuber epiphytes 

 {Myrmecodia, Bolbophyllum); humus-collecting plants with clustered roots {Platy- 

 cenum, Anthuriurn); and plants with aerial roots {Taeniophyllum zollingeri, 

 Angraecuni funale, etc.). 



