B O T A N Y. 



.5.3 



i.ly forms Alburnum, or at least furnishes tl:,- mate- 

 1.;. All this, however, is a mere probability, ai we 



*"V~ ' know very little with certainty connected with it. 



It is difficult to determine by what means the sap 

 u propelled through the vessels: the agitation of the 

 winds, the form of the vessels, the action of heat, th? 

 pressure of certain plates, called silver prain, in the 

 oak, are all supposed to contribute to this end ; and 

 very possibly they do this to a certain extent. We 

 confess, however, that they do not appear to our minds 

 adequate causes. It is a matter of some moment to 

 ascertain how the function is performed ; but our 

 knowledge of facts is so very imperfect, that it is im- 

 possible to frame even a reasonable hypothesis on the 

 subject. In this, as in every other department of phy- 

 sics, men are too prone to step beyond the limits within 

 which their actual knowledge should confine them. 



icunz. Lacuna; are said by Mirbel to exist in vegetables : 



he adds, that they are formed by the laceration of the 

 membranes of the cellular substance, and that they 

 prevail chiefly in water plants, where they seem to pro- 

 mote vigour by diminishing the quantities of absorb- 

 ed fluid, and thus enabling the vessels to perform 

 their functions with better effect. These organs are 

 very well seen in the genus Potamogeto/i. 



lands. It ' s a matter of doubt whether glands exist in 



roots, or in any part of a plant, observation not ha- 

 ving hitherto detected them. The functions, how- 

 ever, which go on in vegetables, render their exist- 

 ence highly probable. M. Mirbel has seen in the 

 stem of the Myriopliyllum, some small fleshy bodies> 

 \vhich may be glands. 



: - cs . Pores penetrate the membranes, and seem to carry 



on, or at least to promote, evaporation and absorp. 

 tion. 



It appears from the preceding detail, that the vas- 

 cular system of plants is annual, which, of course, ex- 

 tends to the roots as well as to every other part. New 

 vessels appear to be annually formed, and to be coeval 

 with the parts that they are destined to nourish and 

 support. How this is performed, it is most improba- 

 ble that we shall ever be able to develope. Hereafter 

 we may discuss more fully all the general facts and 

 deductions which are connected with this most inter- 

 esting, though imperfectly understood, branch of our 

 subject. The preceding details refer, as is sufficient- 

 ly obvious, exclusively to those roots which Willde- 

 now calls rhizomatous. We shall now proceed to 

 examine briefly, the peculiarities of the structure of 

 other roots, which are perhaps of more importance, 

 on account of their various economical uses. The 

 principal roots that we may consider exceptions to 

 the perfect structure, are the following, the .tube- 

 rous and the bulbous. (Part. I. Sect. ii. Art. 4.) 



Of each of these there are several varieties; and it 

 will be sufficient to detail the peculiarities of the most 

 perfect of each, as we have done in the rhizomatous 

 root; and in the first place, we shall mention the 

 tuber. The knobs of which this root is composed, are 

 reservoirs of sap, and of vital energy. Accord- 

 ing to Mr Knight's experiments, they are formed 

 by sap descending through the cortical vessels ; and 

 from some further experiments, the same gentleman 

 lias been led to consider the tuber as performing 

 functions similar to those of the Alburnum of branches, 



except that it raains life with greater tenacity. The < 

 runners from the tuber which rise, are analogous to \ ''> 

 the stem of the plant, and will perform the same *~ 



functions. Tuberous roots are, in general, propaga- 

 t .1 with remarkable ease. In nome instances where 

 there, arc several of them, one of the knobs prodn 

 the herb and flowers of the present year, the next 

 performs the same office in the following year, wlul.- 

 a third is formed to carry on a similar operation 

 in the third year. The root of the Satyrinm alhi- 

 dinn consists of three pairs of tapering knobs, which 

 flower in succession. Dr Smith refutes the usual be- 

 lief, that all the plants of the orchis tribe, which have 

 biennial roots, cannot be transplanted, as he has seen 

 several of them undergo removal when in full flower, 

 without the least injury. The failure in the Saly- 

 rinm albidum is well explained by the same gentle- 

 man, by the fact, that one of its three pairs of knobs 

 is always in a state of activity. 



Bulbs have been already defined, (Part I. Sect, 

 ii. Art. 4.) Their functiprrs are precisely the 

 same with those of tuberous roots. The radicles 

 which they send out, appear to be derived from the 

 sap, which descends from it. It is a singular 

 fact, that some bulbous roots change their cha- 

 racters completely, when removed from the situ- 

 ation in which it is evident that nature designed 

 them to thrive. In general, they inhabit dry, 

 sandy soils, as their structure eminently fits them 

 for resisting drought. The converse of this also 

 happens : Thus the Pklcum pratense has a fibrous 

 root when growing in wet, marshy ground, but on 

 being removed to a dry situation, it acquires bulbs, 

 and becomes the Phleum nodosum. Dr Smith men- 

 tions the same fact with regard to the Alopecurus ge- 

 niculalus. These are not merely curious, but, if pro- 

 perly followed up, may be most important facts for 

 the cultivator. 



All the varieties of roots are adapted to their na- 

 tive soils, and need no particular explanation. We roots, 

 may here mention instar omnium, that the roots of 

 some parasitical plants, chiefly of the genus E/iiden- 

 drum, are thick and fleshy, so that they'are not only 

 firmly attached to the nourishing plant, but are also 

 capable of deriving a larger supply of nutritive mat- 

 ter. All roots do not derive their support from the 

 earth, as those of parasitic plants and of algx. Of the 

 former, the most remarkable is the Epidendrum Jfos 

 aeris, which Loureiro saw in India, vegetating for 

 several years hanging from the ceiling. Although 

 it has been found, that seeds (Part II. Sect, i.) will 

 germinate in almost any material, to which heat, 

 moisture, and air can be added, yet it is equally cer- 

 tain, that they will thrive better in some situations 

 than in others ; and what is very remarkable, the roots 

 will move from an unfavourable to a favourable 

 soil, should they be planted in the immediate vicini- 

 ty of the latter. Mr Knight has lately made some 

 interesting experiments on this subject. He planted 

 parsneps and carrots in a poor gravelly soil, above a 

 rich loam : the radicles of all penetrated to the latter, 

 and fixed themselves eighteen inches below its sur- 

 face. Willdenow mentions this selective property, if 

 it may be so called for the want of a better expres- 

 sion, in a strawberry plant, which being placed in the 



