76 GROWTH AND WORK OF PLANTS 



terns. While there are certain variations and departures from the 

 normal, on the individuals of a given species the arrangement 

 is the same. The arrangement can be studied on leafy shoots, 

 or on winter shoots, since the leaf scars and axillary buds mark 

 the position of the leaves. Leaves are either opposite, alternate 

 or whorled. The pairs of opposite leaves usually alternate at 

 right angles with adjacent pairs. The alternate leaves are 

 arranged in a spiral on the stem; i.e., a line drawn around the 

 stem from left to right and passing over the leaf scars would 

 form a spiral. The arrangement, whether on the opposite or 

 alternate plan, is probably the result of natural causes in the 

 origin of the leaves on the small growing point of the stem, where 

 they are much crowded. The origin in some such regular order 

 whether on the opposite or alternate plan, permits a large num- 

 ber in a given space. Either of these arangements, however, 

 gives the leaves a better light relation, as will be seen in the study 

 of leaves, than if the leaves were arranged promiscuously, or all 

 in a line one above another. 



