232 



ing time, while the dry season is the ripening time, Linsser gives the 

 following general conclusions : 



There are two especial laws regulating the life of every individual 

 plant, (1) the individual habit; and (2) the principle of econom3^ 

 The application of these principles explains and gives us a better 

 comprehension of the course of vegetation under the equator as well 

 as near the pole. 



The principal factors in the life of plants that we have thus far 

 considered are heat and moisture. If the former is that whose 

 periodicity gives warning of the necessity of economy, then the 

 whole life of the plant is intimately dependent on the course of this 

 heat, as in the extreme north and the greater part of the Temperate 

 Zone where the moisture is otherwise sufficient. If it is the moisture 

 that is subject to large periodical changes and the question of suf- 

 ficiency of heat becomes unimportant because of its uninterrupted 

 abundance, then the cycle of vegetable life depends upon the peri- 

 odicity of this moisture, as in Madeira. If, finally, the variations of 

 the climate are such that there is sometimes insufficient heat and 

 moisture, then the necessity of economy in the use of both of these 

 materials is enforced, and in the course of the year the plant seeks to 

 develojD as far as possible in accordance with both these necessities, 

 as in the Steppes of southern Eussia and near Bokhara and in isolated 

 shady locations such as mountain sides. 



The law of fractional parts of the total annual quantit}'^ of heat, as 

 demonstrated in Linsser's first memoir, is therefore now seen to be 

 only a special case, for northern and temperate latitudes, of the gen- 

 eral proposition just enunciated. The former w\as the first approxi- 

 mation toward a rational theory of the periodical phenomena of vege- 

 tation, just as this more general proposition is the second approxima- 

 tion. 



We have thus far studied principally the differences in the life of 

 plants due to differences of climate in different localities. It still 

 remained for Linsser to study the peculiarities of the same plants in 

 different years in the same locality, to which end his manuscript 

 material already offered a sufficient basis. 



Of the questions proper to be considered in this second category, 

 viz, the study of plant life as depending on temporary variations of 

 local climates, Linsser enumerates the following as having already 

 been taken up by him, viz : (1) The influence of cloudiness, insolation, 

 and atmospheric pressure; (2) the especial influence of the various 

 distributions of rain on the individual periods of vegetation; (3) the 

 relation of the length of the da}^ and the night, as also of light 

 itself, on the plant; (4) the influence of the nonperiodic variations 

 of temperature; (5) the influence of cold or warm winters on the sub- 

 sequent summer's growth; (6) the investigation of the sums of tem- 



