566 FORM AND SIZE OF PARTICLES EMPLOYED IN CONSTRUCTION OF PLANTS. 



Naples) plants blossom at the same time as in Marburg, situated 10° further 

 north. 



Stations at which Spring Plants blossom simultaneously. 



3. ULTIMATE STRUCTURE OF PLANTS. 



Hypotheses as to the Form and Size of the Smallest Particles employed in the Construction of 

 Plants. — Visible Structural Activity of Protoplasm. 



HYPOTHESES AS TO THE FORM AND SIZE OF THE SMALLEST PARTICLES 

 EMPLOYED IN THE CONSTRUCTION OF PLANTS. 



When anywhere within the limits of a flourishing town buildings are raised 

 in great number and quick succession by the skilful hands of men, it is said that 

 the houses grow up with astonishing rapidity from the ground. In the same way 

 the growth of plants is appropriately compared by botanists with the erection of 

 human habitations. In this book the latter comparison has already been made as 

 occasion ofiered, and, even at the risk of repetition, I must again make use of the 

 simile here in discussing the building up of plants. 



As in the erection of human habitations, so in the production of the plant 

 structure, it is a question of providing a home for living beings, of securing this 

 home against injury by weather, and other dangers which might terminate the 

 existence of the inhabitants. At the same time the inhabitants in these settle- 

 ments must be able to take in food from the exterior, breathe, work up the food- 

 stufis, and extend themselves further. Where very numerous portions of proto- 

 plasm live, associated together in a plant in social union, and where corresponding 

 to this a division of labour has occurred, the whole structure becomes naturally 

 divided up into open spaces where there is no lack of air and light, into con- 

 trivances for ventilation, into mechanisms for conveying gas and water, and into 

 chambers for storing up nourishment; in short, it is a question of varied mechan- 

 isms within and defences without, of the ensuring of strength throughout the 

 whole structure, and of the necessary supporting framework for the individual 

 parts. Each part occupies a position corresponding to the demand upon it; the 

 light-requiring parts are exposed to the sun's rays; the mechanisms for conveying 



