CONSTRUCTION OF THE SHOOT SYSTEM 6r 



stem, but always occur in vertical or nearly vertical 

 rows. Sometimes only one leaf originates at each node, 

 sometimes two, or occasionally more. When only one 

 occurs the leaves are found to be arranged spirally or 

 alternately up the stem. When more than one there is 

 said to be a whorl of leaves at each node. Frequently 

 the whorl consists of two leaves only. Successive 

 whorls, whatever the number of leaves, have their 

 separate leaves placed opposite the spaces between 

 the leaves of the whorls above and below them. 



The number of the vertical rows is correlated with the 

 shape and size of the leaves which compose them. 

 Leaves with very broad bases, often indented, and 

 tapering fairly rapidly to a pointed apex, known techni- 

 cally as ovate or cordate leaves, generally occur opposite 

 to one another on the stem, there being only two rows. 

 Sometimes they have short stalks, sometimes none. 

 When the leaf has its broadest part near the middle and 

 tapers to both apex and base it is termed an oval or ellip- 

 tical leaf; such are generally arranged in three rows. 

 When still narrower, becoming what are known as 

 lanceolate leaves, the number of rows increases to five or 

 eight. Still narrower leaves occur in greater numbers of 

 ranks still. We see thus a co-ordination between the 

 shapes and dimensions of the leaves and their mode of 

 attachment to the stem, just such a co-ordination as we 

 should expect when we remember the disadvantages 

 which would arise from a crowding together of large 

 ovate leaves in several ranks, or the sparse scattering of 

 linear or narrow leaves in few rows. 



When we study in this way the shoot systems of 

 different plants we find them to be in harmony with 

 their surroundings as fully as are the root systems. The 

 surroundings influence the plant very forcibly while it 

 is developing, and many of the results of its development 

 can only be understood by observing that they are 



