654. DEFINITION AND CLASSIFICATION OF STEMS. 



aubterraiiertii reservoirs. Here they remain quietly deposited during the winter 

 and are not brought into requisition until the plant, at the beginning of the next 

 vegetative period, sends up new shoots which manufacture organic materials 

 afresh. It is in the production of these shoots which are to be sunned above the 

 ground that material is always employed which was conducted down into the store- 

 houses during the preceding year. 



We cannot help surmising that this remarkable alternation between rest and 

 vigorous activity, together with the temporary disappearance of all the aerial por- 

 tions of the plant, is connected with the peculiar conditions of the habitat. This 

 opinion is confirmed by the actual distribution of tuberous and bulbous plants. 

 Most of these plants are found in those regions where all the succulent tissues 

 exposed to the air would be liable to the danger of shrivelling up in consequence of 

 months of drought, and where also the superficial layers of soil in which the tubers 

 and bulbs are embedded dry up so much that they would not be able to replace the 

 water evaporated from the leaves. But when the soil has lost all its water, it forms 

 an excellent protection to the tubers and bulbs; the earth forms an actual crust 

 round the succulent structure, and in many regions the clay soil, coloured red by 

 iron oxide, is hardened into a mass which resembles brick. Embedded in this mass 

 the tubers and bulbs can survive the dry period which lasts over seven or eight 

 months with impunity. When the rainy season comes and the hard crust is 

 moistened, a wonderful life stirs everjnvhere through it. Innumerable tuberous 

 and bulbous plants spring from the softened clay and unfold their flowers and 

 green foliage-leaves during the brief wet period. This is what occurs in the clay 

 steppes of Central Asia, in the mountainous districts of Asia Minor, in Greece, and 

 generally all the countries bordering the Mediterranean Sea. In especial degree is 

 the Cape celebrated for its almost inexliaustible wealth of bulbous and tuberous 

 plants (" cape bulbs "). In Central Europe, where the activity of vegetation is 

 interrupted not by dryness but by frost, the number of these plants is strikingly 

 less than in the districts previously enumerated, whilst the ground in which the 

 few species occur exhibits quite difierent conditions. Here the soil is never exposed 

 to severe drought, indeed, strangely enough, the majority of tuberous and bulbous 

 plants in the depths of the Central European forests are found in loose and dampish 

 earth, rich in humus. It is well known that in such places as these snowdrops and 

 yellow Gagea, the Two-leaved Squill, the purple Martagon Lily, the Cuckoo-pint, 

 the Broad-leaved Garlic, and the various species of Corydalis {Galanthus nivalis, 

 Gagea lutea and G. minima, Scilla bifolia, Liliuni martagon. Arum maculatv/m. 

 Allium ursinum, Corydalis fabacea, G. solida, C. cava), flaunt themselves with a 

 luxuriant and vigorous growth ; and, what is especially worth noticing, their flowers 

 blossom in the first part of the year, their green foliage unfolds early in spring and 

 at midsummer is already yellow and withered, although, as stated, the necessaiy 

 moisture would not be lacking at this season. 



This peculiar phenomenon demands a reason, and we shall not be far wrong if 

 we explain the preference of our early-flowering bulbous and tuberous plants for 



