CHAP, in.] the Movements of Plants. 543 



nutation of the parts of plants.' Under the head of upright or 

 oblique direction of the stem and roots, he speaks of geotropic, 

 heliotropic, and some other curvatures ; then follows a chapter 

 on etiolation, and under the title, ' Movements of plants, which 

 approximate to some extent to the voluntary movements of 

 animals,' he enquires into the periodical and sensitive move- 

 ments of the leaves of Mimosa ; he winds up with a short 

 account of Linnaeus' flower-clock, and of the hygroscopic 

 movements of the valves of fruits. The movements of tendrils 

 and climbing stems, of which Du Hamel seems to have known 

 little, are not mentioned in this connection; but they are 

 noticed in a former chapter with hairs, thorns and similar 

 things, a plan which Cesalpino also adopted. If this way of 

 dealing with the different movements of plants is to be taken 

 as a classification of them, it was a very unsatisfactory one; for 

 it separates like things, and brings together things unlike ; still 

 it is an improvement on Bonnet's arrangement, while the 

 author gives us also some new and valuable observations. He 

 may claim to be the first who made heliotropic curvature 

 depend on light, and it is a significant fact that he got this 

 conclusion from Bonnet's experiments. After examining, like 

 Hales, into the distribution of growth in shoots, and discover- 

 ing that this ceases with the commencement of lignification, he 

 proposed to himself the question : at what spots does the 

 lengthening of the roots take place, and he found from suitable 

 experiments that every root-fibre grows only at its terminal por- 

 tion, which is a few lines in length, and that no other part of it 

 increases in length. In the chapter on the direction of the 

 parts of plants he examines the explanations which had been 

 given of heliotropic curvatures. Astruc and De la Hire had 

 supposed the weight of the descending sap to be the cause of 

 the downward curvature of the roots, and the lighter vapours 

 which ascend in the tissue to be the cause of the upward cur- 

 vature of the stem ; Bazin on the contrary attributed the geo- 

 tropism of the roots to the moisture in the earth. Du Hamel 



