On the Structure of Roots. 475 



of germs of leaves, and the consequent inability to produce buds, 

 is therefore one of the principal negative characters by which 

 roots are scientifically distinguished. 



This character will carry us on pretty smoothly for a lime, but, 

 like all our generalities, it will break down sometimes ; and, 

 indeed, it proves unreliable in some cases very near at hand, and 

 some of no little practical importance. For instance, among trees, 

 we find the alder commonly producing buds and new stems from 

 its roots, certain shrubs are artificially propagated by root-cuttings, 

 and several of our field-weeds have the power, under certain cir- 

 cumstances, of producing buds upon their roots, without the 

 previous occurrence of leaves, in the same abnormal or irregular 

 way as they appear upon cuttings of stems or even leaves of 

 plants in our stoves. 



Seeing that these abnormal or " accidental " buds arise out of 

 the roots in the same way as they do out of the smooth unscarred 

 parts of stems, we are led to inquire how they originate? What is 

 the common peculiarity of stems and roots which enables both to 

 produce and push out their buds ? This is a problem of minute 

 or microscopic anatomy, and when we set ourselves to clear it 

 up, it is not going far aside to apply the same means to ascertain 

 if there exist any more general or any absolutely universal dif- 

 ference between roots, discoverable by the aid of the microscope. 

 Something we shall find in this way. It is almost always pos- 

 sible to distinguish roots from stem-structures by their micro- 

 scopic characters — among the most important of which are the 

 absence of stomata or breathing-pores in the skin of young roots, 

 the absence of a pith and a true fibrous bark in the older roots of 

 both Monocotyledons and Dicotyledons, and a peculiar mode of 

 arrangement of the woody substance in both, by which their 

 respective roots are distinguishable at once from stems and from 

 each other. As the modes of development of the useful roots 

 under artificial treatment, as well as the theory of the part played 

 by the root in the physiological history of plants, can only be 

 comprehended after a thorough examination of the elementary 

 anatomy of roots, we propose to enter upon this presently ; these 

 anatomical characters therefore may be conveniently reserved until 

 we arrive at that portion of our subject. 



Having satisfied ourselves that we can know a root when we 

 see it, let us next turn for a few minutes to the subject of the 

 various forms and conditions in Avhich roots present themselves 

 to us. 



The root exists in a rudimentary condition in the generality (»f 

 seeds, and it is the part which in germination usually first shows 

 signs of renewed life. In the majority, not in all, however, of 

 the class which are called Dicotyledonous plants, the radicle or 



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