Plants as Affected by Excessive Light. 145 



Section IV. Plants as Affected by Unfavorable 



Light. 



A — By Excessive Light. 



235. The Unobstructed Rays of the Sun are often 

 Injurious to young seedlings, to unrooted cuttings and 

 to plants recently 

 transplanted. It is dif- 

 ficult to separate the 

 influences of light and 

 heat, since the heat is 

 usually greatest where 

 the sun's rays are 

 brightest ; but bright 

 light probably stimu- 

 lates transpiration (74) 

 independent of heat 

 and thus tends to exhaust the plant of water. Various 

 devices are used to break the force of the solar rays. 

 In out-door culture, screens of lath (Figs. 61, 62), 



cloth or brush (Fig. 63) 

 are often placed over 

 beds containing cuttings 

 or tender seedlings, as 

 of many cone-bearing 



Fig. 62. Shed screen built of three- trees. CuttingS in the 

 inch-wide slats, for shading tender it, 



plants and for storing pots and boxes nursery may be shaded 



of slow-germinating seeds. (After 



Bailey.) by Supporting a board 



over the row, on short stakes (Fig. 64), so as to protect 

 them during the warmer hours of the day. Shingles, 



Fig. 61. Lath screen used for shad- 

 ing cold-frames and tender plants in 

 the open ground. (After Bailey.) 



