VEGETATION FORMS 177 



rhizomes or winter buds. It is unfortunate, of course, that the term 

 hydrophyte is used here in a much narrower sense than ordinarily. 

 The geophytes, helophytes and hydrophytes are collectively called 

 cryptophytes. 



10. Therophytes (Th). These are the plants which live through 

 the critical season as seeds; that is, they are annual plants. 



It is readily seen that this classification does not take into con- 

 sideration any of the lower forms of plant life. It is further seen 

 that, leaving out of consideration the first two groups, the stem 

 succulents and epiphytes, which in a sense stand apart by them- 

 selves, the remaining groups, beginning with the phanerophytes in 

 Group 3, form a series in which each type has its buds better pro- 

 tected than has the type preceding it. In using this classification 

 for the evaluation of a climate the species of the flora are listed and 

 the percentage of species falling in each group is determined. This 

 list of percentages is spoken of as a biological spectrum and is com- 

 pared with a normal spectrum which is supposed to represent the 

 average conditions for the entire earth. The normal spectrum used 

 by Raunkiaer is as follows : 



In comparing the biological spectrum of any region with the nor- 

 mal spectrum the important feature is the place of greatest deviation 

 from the normal. For example, a study that was made of the flora 

 of New York and vicinity gave the following spectrum : 



The greatest deviation from the normal in this spectrum is found 

 in the large percentage of geophytes and of helophytes and hydro- 

 phytes. Since these three groups together are called cryptophytes, 

 the climate of the region may be called a cryptophytic climate. 

 Some other, rather incomplete, studies that have been made in this 

 country have indicated that the climate of the plains region in the 

 vicinity of Akron, Colorado, is hemicryptophytic, that in Tooele 

 Valley, Utah, chamsephytic, and that of Death Valley, California, 

 therophytic. 



112. Vegetation Forms.— A simple classification into vegetation 

 forms which may be made to include the whole plant kingdom is 

 sometimes found useful. Such a classification, based upon the 

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