142 PLANT LIFE. 



of barbs) into the phloem, and are conducted down 

 into the phloem of the stem or root. The green 

 chlorophyll absorbs the sunlight energy as has been 

 already explained. 



A leaf generally consists of three distinct parts : the 

 flat green blade, the stalk, and the base. It is in the 

 flat portion that most of the carbon-assimilation is 

 carried on, but sometimes the blade is assisted in its 

 work by a flattened stalk (Acacia, Orange), and very often 

 the base of the leaf has a pair of '^stipules''* which, 

 though generally scaly, are sometimes green (Pansy). 



In examining a leaf in the field, it is best to 

 commence by noticing (i) the pattern of the leaves 

 and their individual shapes. Other important details 

 regarding leaves are : (2) their method of over-shading 

 or over-reaching other leaves ; (3) their adaptations 

 for rain ; (4) their protection against wind ; (5) their 

 mechanical support ; (6) their means of defence against 

 insects and fungi ; (7) their arrangement for bud- 

 protection ; and (8) their autumn colours. 



The Daisy is a good example of an over-reaching leaf, 

 which \?> employed as an offensive weapon against other 

 leaves. Any rather neglected pasture will give other 

 good examples of a similar kind. One of the very best 

 is the Cow-parsnip {Heracleum spondyliuni). The leaves 

 appear above the ground in a very humble and tightly 

 folded condition ; but, when the plant is fully developed, 

 the leaves may be eighteen inches long and nine inches 

 broad, and form broad curved arches which cover over 

 the grasses and other plants, and rob them of the sun- 

 light. The Ragwort {Senecio Jacob ed) on its first appear- 

 ance is also very inconspicuous, and the leaves only 

 over-reach their neighbours, when the plant is tall 

 enough to be above their competition. 



