GROUPS 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. Tn one square inch. 
Upper | Under | Upper Under 
si 
side. side. le. side. 
Olive (Olea europea)............ 0 625 0 | 403,125 
Black Walnut (Juglans nigra).... 0 461 0 | 298,345 
Red Clover (Trifolium pratense). 207 885 |133,515 | 216,075 
Lilac aay vulgaris). ... ... 0 330 0 | 212,850 
Sunflower (Helianthus annuus). . 175 825 |112,875 | 209,625 
Cabbage (Brassica oleracea)..... 188 302 | 88,910 | 194,790 
Sycamore (Platanus occidentalis). 0 278 0 | 179,310 
Lombardy Poplar (Populus dila 
PEATE) ia cass foeniese sy 4.8 sy asaya asics 55 270 | 35,475 | 174,150 
Hop (Humulus lupulus)......... 0 256 0} 165,120 
Plum (Prunus domestica)....... 0 2538 0 | 163,185 
Apple (Pirus malus)............ 0 246 0 | 158,670 
Barberry (Berberis vulgaris)..... 0 229 0 | 147,705 
Pea (Pisum sativum) .......... 101 216 | 65,145 | 139,320 
Box (Buxus sempervirens) 0 208 0 | 134,160 
Cherry (Prunus mahaleb)....... 0 204 ‘0 | 131,580 
Thorn-apple(Datura stramonium)| 114 189 | 73,53 121,905 
Indian Corn (Zea mais)......... 94 158 | 60,630 | 101,910 
Cottonwood (Populus monilifera) 89 181 | 57,405 84,495 
Wind-flower (Anemone nemoro- 
BA) is.'s ds mares Oeaioneweenseey 0 67 0} 48,215 
Lily (Lilium bulbiferum)........ 0 62 0; 39,990 
Iris (Iris germanica)............ 65 58 | 41,925 | 38,410 
Oats (Avena sativa).......ee.00s 48 27 | 30,960 17,415 
Practical Studies.—(a) Strip off a bit of the epidermis of a Live- 
for-ever 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. 
(0) 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. 
(c) 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. Note the thickened outer wall of the epi- 
