300 CAIN, DE OLIVEIRA CASTRO, PIRES, AND DA SILVA 



significant to suggest the value of more extensive investigations along similar 

 lines. 



Our tables are so constructed as to present "spectra," or percentage arrays, 

 not only for the life-form classification and leaf-size classification of the 

 total floras of the sample plots, but also for the leaf sizes of each life-form 

 class, and vice versa. 



Raunkiaer employed three guiding rules in the selection of life-form 

 characteristics: (a) the character must be structural and essential; it must 

 represent an important morphological adaptation; (b) the character must be 

 sufficiently obvious that one can easily see in nature to which life form a 

 plant belongs; (c) all the life forms employed must be of such a nature that 

 they constitute a homogeneous system; they must represent a single point 

 of view or aspect of plants and thus enable a comparative statistical treat- 

 ment of the flora of different regions or communities. On a basis of these 

 principles Raunkiaer recognized five life-form classes, with suitable sub- 

 divisions, based on the kind and degree of protection afforded the perennat- 

 ing buds, which are the meristematic tissues responsible for renewal of growth 

 after an unfavorable season. The classes, and the subdivisions we use in this 

 study, are as follows: 



Phanerophytes. In these plants the perennating buds are elevated and 

 exposed to the atmosphere during the unfavorable season. They are mostly 

 woody trees and shrubs, although lianas, epiphytes, and some large peren- 

 nial herbs can be classified here. Because the severity of conditions increases 

 with height above the ground, as a general rule, the phanerophytes are sub- 

 divided into height classes, as follows: 



Megaphanerophytes: With perennial parts, including buds higher than 

 30 m. 



Mesophanerophytes: Between 8 and 30 m. tall 



Microphanerophytes: Between 2 and 8 m. tall 



Nano phanerophytes: Under 2 m. and over 25 cm. tall 



These subclasses can be further divided according to whether the meri- 

 stematic tissues are naked or protected by bud scales and the plants evergreen 

 or deciduous. 



Chamaephytes. Plants of this class are lower than 25 cm. but have their 

 perennating buds definitely above the soil surface. During unfavorable condi- 

 tions these plants may receive some protection from fallen leaves and in 

 higher latitudes considerable protection from snow. 



Hemicryptophytes. The third class has even more protection for its peren- 

 nating buds, for they are located at the surface of the soil where litter, snow, 

 etc., have the greatest chance of covering the buds during dormant periods. 



Cryptophytes. These are the "hidden plants" in which all the aboveground 

 parts die during the unfavorable season and the perennating buds survive 



