126 RELATIONS OF PLANTS TO LIGHT 



3. Transverse section of a velvety leaf of Piper porphyraceum. A layer of 

 aqueous tissue lies next the epidermis of the upper and lower sides. The anthocyan 

 is in the lower half of the leaf. 



4. Mottled leaf of Begonia falcata. a, transverse section of a brownish green 

 velvety shining portion of lamina. The epidermal cells of the upper side are fur- 

 nished with papillose extensions. The epidermal and subepidermal layers are joined 

 without intercellular spaces. The epidermis of the lower side and the spongy pa- 

 renchyma contain anthocyan. b, transverse section through a silvery portion. The 

 outer walls of the epidermis are plane. Large air spaces are present between the 

 epidermis and the cells containing chlorophyl. 



5. Transverse section of a bright spot on the leaf of Ranunculus ficarioides. The 

 subepidermal cells a, contain a few small chloroplasts, and are separated from the 

 layer beneath by large air-spaces. 



6. Papillose epidermal cells of Begonia imperialis, var. smaragdina, seen from 

 above by refracted light. After Stahl. 



Boil a number of colored leaves, Amarantus, in distilled 

 water until a concentrated deeply colored solution is obtained. 

 Test with the spectroscope and note absorption bands, which are 

 not easily made out. Or place a number of red leaves of Coleus 

 in a jar with ether vapor for 20 minutes, then chop fine and ex- 

 tract with distilled water. 1 



192. Relation of Anthocyan to Light. Secure two leaves of 

 Canna or cabbage alike in all particulars except that one contains 

 a large amount of red coloring matter (anthocyan) in addition to 

 the chlorophyl, which is present in about the same quantity as in 

 green leaves. Wrap each leaf around the bulb of a long ther- 

 mometer and expose to sunlight. It is important that the same 

 number of thicknesses of similar portions of the leaves should 

 be interposed between the light and the bulbs. Read the ther- 

 mometers in half an hour and note the influence of the red color. 



193. Arrangements for Concentrating Rays on Chlorophyl. 

 Cut a cross section of a leaf of Coleus, Cissus, Begonia or any leaf 

 showing a velvety upper surface and examine the contour of the 

 epidermal cells. The outer walls are seen to be convex and cap- 

 able of converging all of the rays which strike the surface of the 

 leaf at any angle upon the layer beneath containing chlorophyl. 



1 Muller, N. J. C. Spectralanalyse der Bluthenfarben. Jahrb. Wiss. Bot. 20 : 78. 

 1889. 



