142 Principles of Plant Culture. 



A shade that obstructs only a part of the rays of sun- 

 light at a time, as does the lath or brush screen, is gen- 

 erally preferable to one that continuously breaks the force 

 of all the raj^s, as does paijer or whitewashed glass. 



237. Cauliflower Heads should be Sheltered from Sun- 

 light to prevent the formation of chlorophyll in their 

 cells (40), which darkens their color and gives them a 

 strong flavor. The leaves surrounding the head may be 

 tied about it or broken over s( > as to shade it from direct 

 siinlight. 



B — Plants as Ai-fkcted by Ixsuffictext Light 



238. Insufficient Light is a Frequent Cause of Abnormal 



Development in plants. Some of its effects are 



a — Excessive elongation of the cells of the inteniodes 

 (76), causing the plants to "draw up " or grow spindling. 



b — Deiicient formation of chlorophyll (5S), giving 

 the foliage a pale-green, yellowish or whitish tint, and 

 resulting in 



c — Lessened food formation, causing reduced leaf de- 

 velopment and deficient va.scular bundles ((iS). 



d — Eeduced transpiration tending to watery, weak- 

 celled growth. 



e — Weakening of the color and flavor of some fruits, 

 as the apple and strawberry. 



f — Preventing pollination (151). 



g — Reducing frultfulness. 



0-^\ing to these causes, plants grown in deficient light 

 have tall, slender, -weak stems, few, small, pale k'a\'es and 

 scanty roots and are often unfruitful.* Such plants. 



* Tomato plants grown in winter on poorly-lighted benches are often 

 unfruitful even when they grow well and bloom freely. 



