ELEMENTARY ORGANS. 15 



vn^, or parenchyma ; 2. Pitted tissue, or Bothrcnchyma ; 3. 

 U tissue, or PlcurcjicJn/ma ; 4. Vascular tissue, or Tra- 



rht nc/iyma ; 5. Lactiferous tissue, or Cinenehyma. 



G. Membrane is certainly tlio most important of the tliree 

 priraitnrc conditions of vegotAble substance. It enters into 

 the composition of all the various tissues, and no doubt, forms 

 the great mass of vegetables. Till very recently, it was a 

 point of dispute whether any other existed, but recent inves- 

 tigation seems to have set the subject at rest, as to the real 

 existence of fibre in many cases, and the researches of Mohl 

 and others, have established the existence of organic mucus 

 as a distinct form of vegetable matter, and perhaps a constant 

 one. With respect to the constitution of vegetable mem- 

 brane, two opinions have been held ; one that it is an inor- 

 ganic substance, destitute of fibres, like the fine film compo- 

 sing a soap bubble ; another that it is organized. Du Ham- 

 raell assorted that it was composed of small organic fibres 

 united by a glutinous substance. More recently Lindley and 

 Purkinje have shown — the one that it splits more readily in one 

 direction than another — the other that it tears with a rafrsred 

 edjje. Both facts showinn- that its molecules are arranfjed in 

 such a manner that they adhere more strongly in one direc- 

 tion than the other. Membrane, in its earlv staffe, is ex- 

 tremely thin, but becomes thick by the deposition of other 

 matter. It is entirely destitute of visible pores, nevertheless, 

 is permeable to fluids under certain circum-tanccs. Pores 

 have been described as existing in the membrane, as it com- 

 poses the tissues, but they have more recently been shown to 

 be an optical illusion, except in an instance hereafter to be 

 described. The apparent pores being pits within the mem- 

 brane, making some parts transparent and thinner than oth- 

 ers ; that this is the case, has been proved by chemical action 

 of substances making the membrane opaque when the pores 

 ceased to be discoverable, and all the membrane of a unitbrm 

 appearance. 



7. Elementary Fibre exists in various parts of plants usu- 

 ally united with membranous vessels, and generally assuming 

 a spiral direction. It has not been satisfactorily determined 

 whether it is a simple fibre, or whether it is tubular. Most 

 Botanists, however, consider it a simple, solid fibre. Its ex- 

 treme fineness would lead us to this opinion, since the larf^est 

 kind docs not exceed 1-7000 of an inch. It is not always 

 coiled ; sometimes it ts straiglit, at others curved, and some- 

 times forming a single line ; at others anastomosing, and 

 forming a reticulated tissue, and at others, branchinf]^. It in- 



