42 



manner and form of presentation. A review of the more impor- 

 tant investigations and conclusions that have been reached by 

 various authors prefaces the observations. During the seven 

 years in which the work was prosecuted, ninety-seven species of 

 plants were cultivated in continuous darkness with controls in 

 ordinary alternation of daylight and darkness. Plants illustrating 

 a wide range of habit and habitat were utilized, embracing 

 aquatics, creepers, climbers, succulents, mycorhizal forms and 

 fungi, geophilous and aerial shoots, mesophytes and xerophytes. 

 These were grown from tubers, corms, rhizomes, cuttings of 

 leaves and stems, seeds and spores. A full account of the con- 

 ditions of experimentation, and results obtained with each of these 

 plants is given, together with 176 cuts illustrating the morpho- 

 logical and histological variations. The concluding portion of 

 the volume is devoted to a general consideration and interpreta- 

 tion of the results obtained, and deals with the effect of light and 

 darkness upon the various organs and tissues, the nature of 

 etiolation, the relation of light and darkness to growth and 

 differentiation, the stimulative influence of light, and the influence 

 of etiolation upon chemical composition. An excellent index 

 enhances the value of the book. 



Of the many important features that should be mentioned the 

 limits of this review permit the presentation of only a few. A 

 wide variation is to be seen in the amount of growth or increase 

 in volume, and in the differentiation of the tissues and organs of 

 the etiolated plant. It is interesting to note that in many species 

 the total length, diameter and volume of the etiolated shoot and 

 its organs are not so great as in the case of the plant grown 

 under normal conditions. So also in regard to the differentiation 

 of the tissues, no generalizations can be made owing to the diver- 

 sified conditions found. In a general way it can be said that the 

 degree of differentiation of the tissues is less marked in etiolated 

 forms, and that primary and embryonic tissues, especially paren- 

 chyma, are subject to continued cell formation and growth. To 

 these tissues more especially is the growth and increase in 

 volume due. The abnormal development of this fundamental 

 tissue doubtless also accounts for the commonly observed torsion 



