Pbilomafic Society — Botany » tj^ 



found, that .in: plants really dcflitute of cotytcdohs, fiich as 

 nuifli rooms, the hvffi, fact, Yichftws, and hepatle'a, ho pores ' 

 are found, nor even real bark, nor perhaps epidermis. This 

 abfence of the epidermis explains why miifli rooms arc fo pu- 

 trefcible; why the fuciy&ci -imbibe water To ealily; why 

 coloured water penetrates into the leaves of lichens, which 

 does not take pbcc with other plants. Plants which have, 

 cotyledons have bark : molfes have no cortical pores; ferns 

 have them, biit only below. The monocotyledons with 

 longitudinal fibries have pores between the fibres; and hence 

 the diftingulfliing characters of the different families may be? 

 deduced. The cortical pores ai'e found only on plants or 

 parts of plants expofed to the air, and never on thole v/hich 

 ate under water : immcrfed plants, therefore, are deftitute of 

 them, and flojUing leaves have them only on their upper 

 furface. Decandolle has feen an aquatic ranunculus, which 

 ufually has no pores, acquire a great number when it grew 

 in the open air. He alio made an inverfe experiment, and 

 found that mint, made to grow under water, fent forth leaves 

 without pores. 



Light alfo is necefTarv for the development of pores.' 

 Blanched plants have none; creljes which grew expoled to 

 the light of fix lamps had only half the number they ufu- 

 ally have when in the open ail*. The coats of bulbous roots 

 have none in the parts below ground ; but thofe parts ex- 

 pofed to the light and the air have pories. 



The cortical pores do not ferve for the production of the 

 blue pollen, for plums have no pores; oily plants, which 

 have few pores, have blue pollen in abundance; and from 

 twelve to fifteen thoufand, plants have pores without pro- 

 ducing blue pollen. 



They ferve only for fenfible tranfpiration, for the diverfity 

 of the matters exhaled fecms to indicate a diverfity in the 

 organs : befides, they are found in all vegetables, and that 

 function takes place only in fomc. 



They do not ferve for the efcape of oxygen gas, though the 

 want of them in blanched plants and. the corolle gives reafon 

 to think that they arc deltiued for that purpofe ; but they are 

 found in leaves coloured re(l; which ctT3it..no air : they aro 



Z 2 ■ wantino* 



