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to that of a perfect seed. Twelve or thirteen months elapse 

 between the entrance of the pollen- tubes and production of 

 corpuscles. 



In the Angiosperms, or great mass of flowering plants, 

 the pollen falls on the viscid stigma, the extine bursts, and 

 the intine is protruded as a tube, which pushes on down the 

 style until it reaches the ovule, sometimes a short process 

 rising from the ovule to meet it ; still pushing on, it enters 

 the micropyle and reaches the embryo-sac. Here it comes 

 in contact with the already formed embryonal vesicle, which 

 after impregnation divides into two cells by a transverse 

 partition, the lower forming the embryo- globule, while the 

 upper elongates and becomes the suspensor. 



In the process of impregnation a large amount of oxygen 

 is absorbed and carbonic acid evolved, and an elevation of 

 temperature takes place ; the pollen is shed at the time the 

 greatest amount of heat is produced, and the stamens have a 

 higher temperature than the pistils. In certain orders also, 

 above all in the Araceae, the evolution of heat is most marked. 

 In our common Arum maculatum, during the expansion of 

 the spathe, the temperature has been found to be 15 to 20° 

 above that of the air, in Arum dracuncuhis as much as 31°, 

 but in Colocasia odora growing in the Isle of France, Hubert 

 found that a thermometer in the centre of twelve spadices 

 stood at 142°, while the temperature of the air was 74-75°. 



A far more important point, however, to be borne in mind 

 in the growth of plants, is the absorption of light and heat, 

 since the formation of the tissues, the production of chloro- 

 phyl, the gay tinting of the flowers, the induration of the 

 wood, and all the manifestations of plant-life are solely the 

 result of the transformation of heat into mechanical work ; 

 and never do I muse over my study fire, but the thought 

 ever recurs, that here from the coal-plants is brought back 

 to me, visibly, sensibly, those very sunbeams which shone 



