PRIMARY TISSUES OF PLANTS. 59 



covers all the newly-formed parts of the stem and branches, as 

 well as the various parts of the flower, and even the roots. 



67. These several kinds of structure are termed the primary 

 tissues, being the elements, as it were, of which the edifice is 

 built up ; and they are to the vegetable fabric what the bones, 

 muscles, fat, blood-vessels, nerves, skin, &c. are to the animal. 



68. Even these primary tissues may be regarded as consist- 

 ing of other parts still more simple, namely, membrane and 



fibre. The fleshy portion of the leaf, for example, or the pulp 

 of fruits, consists of a number of little bags adhering together : 

 each bag or vesicle consisting of a delicate membrane, without 

 any perceptible orifice, and containing fluid. The membrane 

 which incloses an egg after the shell is removed, will afford a 

 good illustration, on a large scale, of the nature of these vesicles; 

 they may, however, be readily distinguished and separated in an 

 over-ripe orange, where they are of considerable size. The mem- 

 brane which composes their walls may be regarded as one of the 

 very simplest forms of vegetable tissue. Again, if the stalk of 

 a strawberry or geranium leaf be carefully cut round but not 

 through, and the two parts be then pulled asunder for a short 

 space, a number of glistening fibres, of extreme delicacy, will be 

 seen running from one portion to the other. 

 If these be put under the microscope, it will 

 be evident that they had lain in spiral coils, 

 which are partially straightened when they 

 are thus drawn out, just as when a spiral 

 spring is strained. These were coiled within 

 the membranous tubes, that constitute the 

 external sheath of the spiral vessels, which 

 have been mentioned as existing in the leaf- 

 stalk ; and thus we are able to separate these 

 vessels into the two other elements, membrane FIG. 20. SPIRAL 

 and film. These very minute delicate spiral FIBREsm * AWN OUT - 

 fibres must not be confounded with the woody fibre, of which 

 mention has been made, and the nature of which will be pre- 

 sently explained. 



69. The delicate Membrane, of which, in combination with 



