SHOOTS. 



73 



leaves that no peculiar stem type is developed. In the 

 pines scale leaves are found abundantly on the stems which 

 are developed for foliage purposes. In fact, the main stem 

 axes of pines bear only scale leaves, while short spur-like 

 branches bear the characteristic needles, or foliage leaves, 

 but the form of the 

 stem is controlled 

 by the needs of the 

 foliage. Some very 

 distinct types of 

 scale-bearing stems 

 may be noted. 



50. The bud type. 

 — In this case the 

 nodes bearing the 

 leaves remain close 

 together, not sepa- 

 rating, as is neces- 

 sary in ordinary 

 foliage-bear ing 

 stems, and the 

 leaves overlap. In 

 a stem of this char- 

 acter the later joints 

 may become sepa- 

 rated and bear foli- 

 age leaves, so that 



one finds scale leaves below and foliage leaves above on 

 the same stem axis. This is always true in the case of 

 branch buds, in which the scale leaves serve the purpose 

 of protection, and are aerial, not because they need a 

 light-relation, but because they are protecting young foli- 

 age leaves which do. 



Sometimes the scale leaves of this bud type of stem do 

 not serve so much for protection as for food storage, and 

 become fleshy. Ordinary bulbs, such as those of lilies, etc., 



Fig. 63a. Cotyledons of castor-oil bean ; the seedling 

 to the left showing the ordinary position of the 

 cotyledons, the one to the right showing the curva- 

 ture of the stem in response to light from one 

 side. — After Atkinson. 



