LIFE-FORMS. 59 



IV. Cryptophytes (bud-shoots buried in the soil): 

 Geophytes : 



23. Rhizome geophytes: Polygonatum. 



24. Tuber geophytes: Cyclamen. 



25. Tuberous root geophytes: Orchis. 



26. Bulb geophytes: Allium, Lilium. 



27. Root-bud geophytes: Cirsium arvense, Moneses. 



28. Helophytes: Typha, Scirpus, Equisetum, Sagittaria. 



29. Hydrophytes: Nymphaea, Zostera, Hippuris, Potamogeton. 

 V. Therophytes (3); annuals: Galium aparine, Thlaspi arvense. 



Warming, 1908. — Warming (1909 : 5) has based his outline of growth- 

 forms upon the following principles: 



"Just as species are the units in systematic botany, so are growth-forms the 

 units in oecological botany. It is therefore of some practical importance to 

 test the possibility of founding and naming a limited number of growth-forms 

 upon true oecological principles. It can not be sufficiently insisted that the 

 greatest advance not only in biology in its wider sense, but also in oecological 

 phytogeography, will be the oecological interpretation of the various growth- 

 forms: From this ultimate goal we are yet far distant. 



"It is an intricate task to arrange the growth-forms of plants in a genetic 

 system, because they exhibit an overwhelming diversity of forms and are 

 connected by the most gradual intermediate stages, also because it is difficult 

 to discover guiding principles that are really natural. Nor is it an easy task 

 to find short and appropriate names for the different types. Genetic rela- 

 tionships and purely morphological or anatomical characters such as the vena- 

 tion and shape of leaves, the order of succession of shoots, monopodial and 

 sympodial branching, are of very slight oecological or of no physiognomic 

 significance. Oecological and physiological features, particularly the adapta- 

 tion of the nutritive organs in form, structure, and biology, to climate and sub- 

 stratum, or medium, are of paramount importance. Cases are not wanting, how- 

 ever, in which oecological grouping runs parallel with systematic classification. 



"In the case of the polycarpic plants it is necessary to consider, first, their 

 adaptation to climate, and in particular the season unfavorable to plant life; 

 secondly, the vegetative season ; and finally the conditions prevailing in regard to 

 the soil, which Schimper terms edaphic conditions. Of greatest importance is — 



" 1. Duration of the vegetative shoot: Lignified axes of trees, shrubs, and under- 

 shrubs; perennial herbaceous shoots; herbaceous shoots deciduous after a 

 short period. 



"And closely associated with this is — 



"2. Length and direction of the internodes: Whether the shoots have short 

 internodes (rosette-shoots) or long internodes, and whether the latter are 

 erect (orthotropous) or prostrate and creeping (plagiotropous). 



" 3. Position of the renewal buds during the unfavorable season high up in the 

 air, near the soil, under the surface of the soil, or buried in the soil (geophilous). 



"Of less importance is — 



"4. Structure of the renewal-buds or of buds in general. 



" 5. Size of the plant is of some moment, not only because in the struggle for 

 existence the taller plants are enabled to establish a supremacy more easily, 

 but also because they are more exposed to the inclemency of climate; shrubs 

 reach greater altitudes and latitudes than trees, while dwarf shrubs and 

 herbs extend even further than shrubs. 



"7. The adaptation of the assimilatory shoot to the conditions of transpiration. 



"8. The capacity for social life is of great importance in the struggle between 

 species and consequently in the composition and physiognomy of the plant- 



