26 BOTANY part i 



Potato plant remain in the ground and give rise to a large number 

 of new plants, it is of great advantage to the new generation that 

 the tubers are produced at the ends of runners, and are thus separated 

 from one another. 



The Metamorphosis of Aerial Shoots. — Similar advantages to 

 those obtained by the elongation of the underground shoots in the 

 Potato accrue from surface runners, such as are produced on Straw- 

 berry plants. Surface runners also bear scale-like leaves with axillary 

 buds, while roots are developed from the nodes. The new plantlets, 

 which arise from the axillary buds, ultimately form independent 

 plants by the death of the intervening portions of the runners. 



Tlie runner of Fragaria collina is a monopodiuni, a single elongated shoot, 

 from the axillary buds of which the new plants arise. In other species of 

 Strawberry the runner is a sym podium, the elongated shoot terminating in a rosette 

 of foliage leaves and the runner being continued by the axillary bud of the 

 lowest of the leaves of the rosette Q-). 



A striking modification is exhibited by shoots which only develop 

 reduced leaves, while the stems become flat and leaf-like and assume 

 the functions of leaves. Such leaf-like shoots are called cladodes 

 or PHYLLOCLADES, and Groebel proposes to distinguish those flattened 

 shoots which have limited growth and specially leaf-like appearance 

 as phylloclades, and to term other flattened axes cladodes. Instruct- 

 ive examples of such formations are furnished by Eiiscus aculeatus 

 (Fig. 27), a small shrub whose stems bear in the axils of their scale- 

 like leaves (/) broad, sharp-pointed cladodes (c/) which have altogether 

 the appearance of leaves. The flowers arise from the upper surface 

 of these cladodes, in the axils of scale leaves. In like manner the 

 stems of the Opuntias (Fig. 28) are considerably flattened, while the 

 leaves are reduced to small thorny protuberances. In this case the 

 juicy flat shoots perform not only the functions of assimilatory 

 organs, but also serve as water-reservoirs in time of drought. 



On the other hand, a plant may lose its leaves more or less com- 

 pletely without any marked flattening or thickening occurring in the 

 stems, which then take on a green colour ; this, for example, is the 

 case in the Broom {Spartium scoparium) which develops only a few 

 quickly falling leaves on its long, naked twigs. As a rule, however, 

 leafless green Phanerogams will be found to have swollen stems, as in 

 the variously shaped species of Euphorhia and Cactus. 



Reduction of the Shoot in Parasites.--A great reduction in the 

 leaves, and also in the stems, often occurs in phanerogamic parasites,, 

 in consequence of their parasitic mode of life. The leaves of the 

 Dodder {Cuscula, Fig. 196 b) are only represented by very small 

 yellowish scales, and the stem is similarly yellow instead of green. 

 The green colour would, in fact, be superfluous, as the Dodder does 

 not produce its own nourishment, but derives it from its host plant. 



