GUOUPS OF TISSUES, OR TISSUE-SYSTEMS. 39 



The number of breathing-pores has been determined for many- 

 leaves. The following table will give an idea of their abundance on 

 some common leaves: 



In one square 

 millimetre. 



Upper 



side. 



Under 

 side. 



In one square inch. 



Upper 

 side. 



Under 

 side. 



Olive (Olea europea) 



Black Walnut (Juglans nigra).. . . 

 Ked Clover (Trifoliumprateuse). 



Lilac (Syringi vulgaris) 



Sunflower (Helianthus annuus). . 



Cabbage (Brassica oleracea) 



Sycamore (Platanus occidentalis). 

 Lombardy Poplar (Populus dila 



tata) 



Hop (Humulus lupulus) 



Plum (Prunus domestica) 



Apple (Pirus malus) 



Barberry (Berberis vulgaris) 



Pea (Pisum sativum) 



Box (Buxus sempervirens) 



Cherry (Prunus mahaleb) 



Thorn-apple(Datura stramonium) 



Indian Corn (Zea mais) 



Cottonwood (Populus monilifera) 

 "Wind-flower (Anemone nemoro 



sa) 



Lily (Lilium bulbiferum) 



Iris (Iris germanica) 



Oats (Avena sativa) 









 207 





 175 

 138 







55 

 

 

 

 



101 

 

 



114 

 94 











65 



48 



635 

 461 

 335 

 330 

 335 

 303 

 378 



370 

 356 

 353 

 346 

 339 

 316 

 308 

 304 

 189 

 158 

 131 



67 

 63 



58 



37 











133,515 







113.875 



88,910 







35,475 



















65,145 











73,530 



60,630 



57,405 











41,925 



30,960 



403,135 

 398,345 

 216,075 

 213,850 

 309,635 

 194,790 

 179,810 



174,150 

 165,130 

 163,185 

 158,<i70 

 147,705 

 139.330 

 134,160 

 131,580 

 131,905 

 101,910 

 84,495 



43,315 

 39,990 

 38,410 

 17,415 



Practical Studies. — (a) Strip off a bit of the epidermis of a Live- 

 forever leaf. Mount it in alcohol to avoid air-bubbles, and after- 

 wards add water and a little potassic hydrate. Epidermal cells and 

 breathing-pores may be well seen. 



(i) Prepare in like manner the epidermis of both upper and under 

 surfaces of a cabbage-leaf. Note the breathing-pores on both sur- 

 faces; note also the bloom. 



(o) Make very thin cross-sections of a cabbage-leaf (by placing a 

 piece of leaf between two pieces of elder-pith) so as to secure cross- 

 sections of the epidermis, l^ote the thickened outer walj of the epi- 



