THE PKOPAGATJON OV PLANTS, WITHOUT SEEDS. 299 



The question arises, why are some forms thick and fleshy, while 

 others, as the last named, are long and slender ? 



There are good reasons for assuming such to have arisen through the 

 <;haracter of the soil, whether it be "stiff" in the former case or loose in 

 the latter. In this case they will run to grtat lengths of many feet. 



In species of Mint, after the terminal bud has arisen above-ground 

 in summer to make the annual aerial flowering-stem, it will send out 

 numerous lateral subterranean shoots ; but if one or more happen to be 

 Just above-ground they will take the form of aerial runners. This fact is 

 very suggestive of the origin of runners in such plants, in which they 

 now habitually occur, without subterranean creeping stems at all, as of 

 'Strawberries, Ranunculus repens, &c. 



With regard to the origin of corms, tubers, &c., it is probable that these 

 ^ire due to their having originally grown in a heavy soil, for there is no 

 reason to suggest a dift'erent cause for such stems from that which is known 

 to produce " long " and " short " roots in Radishes, Carrots, Turnips, &c.* 



Bulbs are usually subterranean buds, consisting of short, fleshy bases 

 <of leaves, inserted upon a conical axis, which may terminate with either 

 :a flower-bud or leaf-bud. 



The bulb-scales are, of course, storehouses of nutriment for future use. 



How did they arise ? 



That a part of a petiole of a leaf should remain on the stem with its 

 <:ells full of starch, while the rest of the leaf-stalk with the blade falls oft', 

 is not unknown. Such is the case with our Wood-sorrel {Oxalis 

 Acetosella). 



Now, if the bud in the axil of a leaf receive and store up the nutri- 

 ment, its rudimentary leaves become thick scales. This is the case with 

 other species of Oxalis. But in many of the Stone-crop family 

 {Crassulacece) the buds are green and become "offsets" on stolons, 

 -capable of being detached and of growing into new plants. 



Li Sedum dasyplnjllum a single leaf may be detached and carry 

 -away a minute bud at its base, and supply water and nutriment to the 

 latter until it is independent, by having developed roots of its own. 



In Lilium hulhiferum and some other plants the bulb-scales are more 

 compact, only the surface remaining green, and as the stem decays they 

 fall oft' and will then reproduce the Lily. , 



It is more common, however, to find bulbs on underground stems, 

 generally proceeding from the axils of the parent bulb-scales, as in Lilies, 

 Hyacinths, Garlic, &c. Sometimes they are borne by creeping stems, 

 whether above or below ground, as on those of Oxalis cernua. 



We see here a compensating process. In the long, creeping stems, or 

 stolons, which send up tufts of leaves at each node, as on a Strawberry- 

 runner, Sand-grasses and Sedges, &c., there is no need to store up more 

 food than the stem can contain. As soon as roots are formed each node 

 produces an independent plant. In Oxalis cernua the creeping stem is 

 very slender and perishes in the dry season : so ias soon as the plant dies 



* Pliny tells us that the Greeks discovered how to change the " female " or long- 

 rooted Rape into the "male" or round form by sowing the seed in a cloggy soil. 

 M. Carriers" ennobled " the wild Eadish,and found long forms were mainly produced 

 in a light soil, and more or less round roots in a stitY one. M. Languet de Sivry 

 experienced similar results with Carrots. See Origin of Plant Structures, p. 180. 



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