2 ORGANOGRAPHY. BOOK I» 



It is the opinion of some that membrane only is the basis of 

 the tissue of plants, and that fibre is itself a form of mem- 

 brane. But as we find both developed in many of the most 

 imperfectly organized plants, such as Scleroderma and other 

 fungi, and as it is difficult to conceive how that can be a 

 mere modification of membrane which is generated inde- 

 pendently of it, which has no external resemblance to it, and 

 which is obviously something superadded, it will be better to 

 consider both membrane and fibre as the organic bases of 

 vegetable tissue, rather than the former only. 



The membrane varies in its degree of transparency, being 

 occasionally so exceedingly thin as to be scarcely discover- 

 able, except by the little particles that stick to it, or by its 

 refraction of light, and sometimes having a perceptible green 

 colour, and a thickness which is considerable if compared 

 with the diameter of the cavity it encloses. It is always ex- 

 cessively thin when first generated ; and whatever thickness it 

 afterwards acquires must be supposed to be owing to the 

 incorporation or incrustation of secreted matter. This is 

 I'epresented by Mohl to take place in Palm-trees by the succes- 

 sive addition of strata to the lining of the cavities of the cells ; 

 but this requires verification. 



It generally tears readily, as if its component atoms do not 

 cohere with greater force in one direction than another ; but 

 I have met with a remarkable instance to the contrary of this 

 in Bromelia nudicaulis, in which the membrane of the cuticle 

 breaks into little teeth of nearly equal width when torn. 

 (Plate I. fig. 6.) Hence it maybe conjectured, that what we 

 call primitive membrane is itself the result either of primitive 

 fibres completely consolidated, or of molecules originally dis- 

 posed in a spiral direction, as Raspail supposes. {Chim. Org. 

 p. 85.) 



It is in all cases destitute of visible pores ; although, as it is 

 readily permeable by fluids, it must necessarily be furnished 

 with invisible passages. An opinion to the contrary of this 

 has been held by some botanists, who have described the 

 existence of holes or pores in the membrane of tissue, and 

 have even thought they saw a distinct rim to them ; but this 

 idea, Mhich probably originated in imperfect observation with 



