184 Prof. Henfrey on the Development of Roots, 



would be of high importance to the development of our know- 

 ledge. 



However the results at which we have arrived may he re- 

 ceived, we have only searched for truth. The laws that we have 

 developed as resulting from a geological theory, had revealed 

 themselves long since to our eyes in nature; for during many 

 years we have ever been guided by one single motive — 



'' Natm^d doceriJ' 



XIX. — On the Development of Roofs, and the Exfoliation of the 

 Cellular Coats of their Extremities, By Arthur Henfrey, 

 P.R.S. 



In the ' Journal of the Royal Agricultural Society of England,' 

 vol. xix. part 2, published in January last, there is an essay on 

 the Structure of Roots, by myself, in the latter part of which is 

 described the mode in which the extremities of roots elongate, 

 and the special arrangements by means of which they are 

 enabled to penetrate the soil. The same subject has more re- 

 cently been dealt w^th by MM. Garreau and Brauwers, who 

 appear to have been ignorant of the existence of my paper above 

 referred to ; these authors have made some extensive investiga- 

 tions on a further point connected with these root-ends, viz. the 

 possibility that the exfoliated tissue may constitute an excretion 

 capable of exerting an injurious influence upon the same species, 

 and so account for some of the most puzzling phsenomena re- 

 lating to the rotation of crops. As the subject is one of great 

 physiological interest, it may be worth while to extract from the 

 ^Agricultural Journar those portions of the above-mentioned 

 essay which relate to the anatomy and development of roots, at 

 the same time that I present a translation of the memoir of 

 MM. Garreau and Brauwers. The statements in my own paper 

 are made in somewhat general terms, as it was prepared for a 

 somewhat ^'popular^^ class of readers; but they were based upon 

 an original series of investigations which furnished facts in all 

 respects identical with those related in detail by the French 

 authors, to whom, however, exclusively belongs the merit of that 

 part of the inquiry concerning the nature of the substances cast 

 off' by the exfoliating radicles. 



" The root, as developed in the great majority of plants, pre- 

 sents a highly organized structure, made up of various kinds of 

 true cellular or parenchymatous tissue, together with those kinds 

 of elementary tissue which, under the names of wood-cells, ves- 

 sels, and ducts, form the hard parts of plants. As a rule, we 

 may divide the internal structures of a root into two regions — 



