480 THE POPULAR SCIENCE MONTHLY. 



tective property of adaptation to desiccation so rarely appear 

 among the higher plants ? — why have the plants of the steppes 

 and deserts, for example, to protect themselves against the perils 

 of drought by so various anatomical features, of thick skins, corky 

 bark, waxy and hairy envelopes, receptacles for water, etc., instead 

 of simply drying up and reviving again in the rainy periods ? 

 The answer to the question is not hard to find. The maxim, " one 

 thing is not suitable for all," is valid in the biological domain. 

 That which works well in the little mosses is for various reasons 

 not available to the larger phanerogams. First, the larger plants 

 must continue to vegetate actively for longer periods, in order to 

 prepare the amount of food required for the proper growth of 

 their organs. Ever-recurring interruptions of their feeding by 

 drying out would so retard the whole process of their growth, 

 that in spite of their vital tenacity they would be at a great dis- 

 advantage in the struggle for existence. To this is added another 

 not less weighty reason, that the mosses are so simple in their 

 anatomical structure that the mechanical shrinking of the drying 

 tissue involves no danger ; the collaborated cells easily resume 

 their original form and size on the accession of a new water- 

 supply. It is very different with the organs, far more compli- 

 cated in their structure and composed of tissue of diversified 

 kinds, of the more highly developed plants. In them extensive 

 shrinkage would result in damaging tensions and distortions, and 

 even cracks, for the limitation of which various mechanical pro- 

 tective adaptations would be required. Besides this, the mechani- 

 cal structure of the tissues would have to have a proportionately 

 enormous development, else the dry, brittle leaves and branches 

 would be broken U23 by every gust of wind. A careful regard to 

 the consequences of such an adaptation to complete desiccation 

 should be sufficient to convince any one that it would be too 

 dearly purchased. But in the case of many of the humbler plants 

 insensibility to continuous desiccation is a life-question, and ac- 

 cordingly they have practically acquired that property. It is of 

 equal interest from a physiological and a biological point of view 

 that the protoplasm of the young individual should, by further 

 development, gradually suffer the complete loss of so pregnant a 

 property as that of reviving after it has been dried up. 



The power of the mosses to endure repeated desiccation has 

 recently been experimentally treated by G. Schroder,* who ob- 

 tained the interesting result that many of these plants can not 

 only resist months of dryness without any harm, but also that 

 they do not perish even under the strongest desiccation carried 

 on in a drier with the aid of sulphuric acid. Plants of Barbula 



* " Ueber die Austrocknungsfahigkeit der Pflanzen." Untersuchen aus dem bolanischen 

 Institut zu Tubingen. Published by Pf offer. Vol. ii, part i, 1886. 



