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 rays, as does paper 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 so as to shade it from direct 

 sunlight. 



B PLANTS AS AFFECTED BY INSUFFICIENT 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 internodes 

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



b Deficient formation of chlorophyll (58), giving 

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

 resulting in 



c Lessened food formation, causing reduced leaf de- 

 velopment and deficient vascular bundles (68). 



d Reduced 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 fruitful ness. 



Owing to these causes, plants grown in deficient light 

 have tall, slender, weak stems, few, small, pale leaves and 

 scantv 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. 



