1^5 On the Anatomy of Vegetables. 



tracheae, is not rigorous. In eftablifhing it, I do not pre- 

 tend to atfign immutable laws of nature ; I have had occafum 

 to obferve that it often deviates from them. Thus the bu- 

 tomus umbellaliis exhibits in the fame tube the pores of the 

 porous tubes, the flits of the falfe tracheae, and the fpirals 

 of the true tracheae ; fo that one tube comprehends three of 

 the modifications I have defcribed. Thefe tubes I call the 

 mixt. Other vegetables exhibit fomcthing analogous or in 

 fimilar (ituations, there are found in them one of the four 

 varieties of the large tubes. It is not uncommon to fee all 

 thefe tubes cloiely united the one to the other, and forming 

 only one tiflue. In a word, it may be conjectured, with 

 fome appearance of reafon, that in many cafes the tracheae 

 unroll thcmfelves only becaufe the membranes which unite 

 their fpirals are torn. Let us conclude then that thefe dif- 

 ferences, which on the firfl: view appear of fo much import- 

 ance, are only flight (hades in the vegetable economy. But 

 the large tubes, confidered in a more general manner, pre- 

 fent themfelves to the mind as the creative organs; their nu- 

 merous ramifications diiiributed throughout all the parts of 

 the vegetable carry thither the vivifying juices ; by thefe the 

 item acquires more vigour, the bud is produced, pierces the 

 bark, and lengthens under the form of a branch ; the leaf 

 expands, the flower blows, and the fruit fwells up and ripens, 

 while the embryo concealed in its bofom receives its firfl: nu- 

 tritive juice's. 



Article II. 



Of the fmall Tubes. 



Thefe are compofed of cells united to each other like thofe 

 which compofe the cellular tiflue; but in the cellular tiflue 

 the diameter of the cejls is nearlv equal in every direction ; 

 while in the former the cells are much elongated, and form 

 real tubes, the extremities of which are (hut: the fides alfo 

 are lefs transparent, and the membranes of which they are 

 formed have more confidence : thev are often perforated with 

 a great number of pores. This tiflue is thick, folid, and te- 

 nacious. It is generally difficult to cut it through ; but it 

 preients much lefs refinance lcngthwife, and often feparates 

 eafily into threads of greater or lefs delicacy, and which verv 

 improperly have been called fibres. The folidity of the vege- 

 table depends in particular on the quantity and denfity of this 

 rifliie : it contains, according to the fpecies in which it is 

 found, fometimes thick and coloured juices, but fometimes, 

 mtxi niore commonly, limpid and colourlefs juices. In the 



fir 



