1 8 The Ottawa Naturalist. | April 



ON THE STRUCTURE OF ROOTS. 



By Theo. Holm. 



It i. a general belief that plant-roots exhibit but very lew 

 modifications in regard to function and structure, and almost as a 

 rule the histology of this organ is silently passed by in works on 

 plant-anatomy. Furthermore, it is a very common feature of 

 herbarium specimens that the parts underground, for instance the 

 roots, are either totally absent or poorly preserved. It is, there- 

 fore, often very difficult to study roots in herbaria, and the student 

 is mostly obliged to secure the material himself and to make alcohol 

 preparations. When roots are dried and pressed they may in some 

 cases be made useful to histological research by heing placed in 

 boiling water and then preserved in strong alcohol, but many 

 roots, especially the fleshy ones, loose their delicate structure to 

 such an extent when they are dried and pressed, that they are not 

 suitable for this purpose. If the herbalists would preserve parts 

 of the various organs of plants in alcohol as an appendix to their 

 herbaria, the plants might be studied more carefully and from 

 other points of view than merely systematically. 



To give some illustration of the various functions performed 

 by roots, we might refer to a modern and very suggestive paper by 

 our excellent friend Dr. August Rimbach,* in which the following 

 four types are proposed: "nutritive," "attachment," "con- 

 tractile," and " storage-roots." 



Roots of the first type possess no pronounced power of resist- 

 ance, since they have no mechanical tissues, nor are they con- 

 tractile nor especially adapted " to store " nutritive matters. 

 They are generally very slender and certain plants possess only 

 this type, for instance : Dentaria, Tulipa, the Graminece and many 

 others. 



The second type, the attachment-roots, needs no further ex- 

 planation, and these we know from the epiphytic BromeliacecB. 



The contractile roots have th power of contracting, thus 

 drawing the shoot deeper and deeper into the ground, as for in- 

 stance : Scilla, Crocus, Gladiolus, some species of Oxalis, etc. 



Storage-roots are, on the other hand, such roots as possess 



* Berichte Deutsch. Bot. Gesellsch. Vol. 17. Berlin 1899. 



