MORPHOLOGY 25 



thickened scale leaves (zs) of which are filled with reserve food 

 material. The aerial growth of a bulb develops from its axis, while 

 new bulbs are formed from buds (k) in the axils of the scale leaves. 

 Another form of underground shoot, allied to bulbs and connected 

 with them by transitional forms, is distinguished as a TUBER. The 

 axis of a typical tuber, in contrast to that of a bulb, is fleshy and 

 swollen, serving as a reservoir of reserve material, while the leaves 

 are thin and scaly. Of such tubers those of the Meadow Saffron 

 (Colchicum autumnale) or of Crocus sativus are good examples. In the 

 Meadow Saffron new tubers arise from axillary buds near the base of 

 the modified shoot, but in the Crocus from buds near the apex. In 

 consequence of this, in the one case the new tubers appear to grow 

 out of the side, and in the other to spring from the top of the old 

 tubers. The tubers of the Potato (Fig. 26) or of the Jerusalem 

 Artichoke (Helianthus tuberosus) are also subterranean shoots with 

 swollen axis and reduced leaves. They are formed from the ends of 

 branched, underground shoots or runners (STOLONS) and thus develop 

 at a little distance from the parent plant. The so-called eyes on the 

 outside of a potato, from which the next year's growth arises, are in 

 reality axillary buds, but the scales which represent their subtending 

 leaves can only be distinguished on very young tubers. The parent 

 plant dies after the formation of the tubers, and the reserve food 

 stored in the tubers nourishes the shoots which afterwards develop 

 from the eyes. Since, in their uncultivated state, the tubers of the 

 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. 



Still more marked is the modification 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 PHYLLOC LADES, and Goebel proposes to dis- 

 tinguish those flattened shoots which have limited growth and specially 

 leaf-like appearance as phylloclades, and to term other flattened axes 

 cladodes. Instructive examples of such formations are furnished by 

 Ruscus aculeatus (Fig. 27), a small shrub whose stems bear in the 

 axils of their scale-like leaves (/) broad, sharp-pointed cladodes (cl), 

 which have altogether the appearance of leaves. The flowers arise 

 from the upper surface of these cladodes, in the axils of scale leaves. 



