926 



A TEXTBOOK OF THEORETICAL BOTANY 



AXIS AXIS 



Fig. 908. — Asparagus officinalis. A, Shoot showing the arrangement of the needle-like 

 cladodes in reduced axillary cymes. B and C, Diagrams illustrating the order of develop- 

 ment of the cladodes in a cyme. (B and C after Eic hi er.) 



Pear), the shoots of which form large discoid segments (Fig. 909). The apex 

 is, however, radially symmetrical, and in some species all the shoots are 

 globose or cylindrical. Some other species of the Cacti are also flattened, 

 notably among those which form the genus EpiphyUum, frequently grown for 

 the sake of its large scarlet flowers. None of these Cacti has any true leaves. 

 This is probably connected with their desert habitat, but the flattened shoots 

 are a peculiarity of these genera, not necessarily related to the environment. 



In the genus Muehlenheckia (Polygonaceae) and Carmichaelia (Papilio- 

 naceae) (Fig. 910), from the southern hemisphere, the shoots may form jointed 

 green ribbons, but temporary leaves are produced at the nodes in spring. 



Certain species of Phyllanthus (Euphorbiaceae) show an interesting 

 example of what we may call pseudo-phylloclades. The main shoots bear 

 only scale leaves from whose axils arise side shoots of limited growth, which 

 are pinnately branched and bear small true leaves in two lateral rows. The 

 whole appearance of these shoots is exactly that of the pinnately compound 

 leaves of such leguminous plants as Mimosa. In other species of Phyllanthus 

 the lateral shoots are true phylloclades. 



2. Thorns. True stem thorns are distinguished from prickles by their 

 branch nature (Root thorns, see p. 824). 



Prickles are modified trichomes (see p. 869), and spines are usually 



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