Special cases may be distinguished, as : 



Rhizome of many forms, as in Iris ; the main axis remains prostrate at soil 

 level, or even below, out of the way of desiccation, sending up erect foliage-leaves 

 and inflorescences under optimum Spring conditions : essentially an adaptation to hot 

 desert with sandy soil. Note short seasonal growths, leaf-scars, advt. roots, and 

 utilization of stem-tissues for storage of reserves, as starch. Perennation over 

 summer heat may be continued over winter cold as well. By further concentration of 

 shoot-system and deeper soil-penetration the case of the ' bulbous ' Iris, with starch- 

 storage in leaf-members. 



The Tuber (cf. Potato, Artichoke) as a special case of subterranean shoot- 

 formation, i or more internodes of a rhizome-system being swollen, filled with food- 

 reserves in parenchymatous tissues, and readily separated from parent plant. More 

 or less rounded form ; succulence due to water-storage ; with corky covering ; 

 enduring desiccation, and also utilized for dispersal. 



Potato (Solarium tuberosuni), a plant of Central America adapted for perennation 

 over hot dry season in sand, to germinate in wet season ; tubers originally small 

 (i in.) and round. Utilized in this country for perennation over cold winter (under 

 cover), and often grown in clay soil : cf. stem-structure, stalk-end and apical crown 

 with T-system of leaf-scales and buds (' eyes '), or scars of subtending leaves ; 

 section near stalk shows V.B. distributed; delimiting cortex and broad central 

 medulla. Spiral vessels in V.B. (test phloroglucin -H 2 SO 4 ), and large starch-grains 

 (to 90 //,) with conspicuous stratification and eccentric hilum. 



The Corm : cf. Crocus as a more extreme case ; the entire plant dried off and 

 reduced to a solid short main axis, with dense starch-storage ; enclosed in dead scale- 

 leaves, with lateral buds (i or more); these break out as flowering leafy shoots in 

 spring : cf. Yellow Crocus with white scale-leaves, green foliage-leaves, and 1-3 

 flowers in each such shoot. Plants dug up in March show new corm forming at the 

 base of each new shoot. Cf. Montbretia, similar enlargements of successive seasons 

 remain attached in linear series. 



The Bulb (Lilium, Narcissus, Hyacinthus), a limiting case in which the entire 

 plant is reduced to one perennating bud-construction : cf. Narcissus ; reduced axis at 

 base of bulb giving off adventitious roots ; bulk of structure as a mass of leaves, 

 functional in successive seasons as (i) dead scales remaining as protective wrapping; 

 (2) storage-leaves, with starch and mucilage ; (3) young leaves of next season, pale 

 green, with no storage ; (4) in section of apex only, rudiments of a few primordia of 

 another season. (Differentiate by Iodine sol.) 



In fine bulbs note central flower (Narcissus), or inflorescence with many buds 

 (Hyacinthus). In Narcissus the flower is lateral, and the apex, at its base, follows on : 

 in Lilium and Hyacinthus the flower spike is terminal, and a lower axillary bud takes 

 on the new growth. The adaptation for summer rest in sandy soil is, in this country, 

 continued over the cold winter, and such plants vegetate in spring only, on a short 

 season (April-June), fruiting and seeding before midsummer; though exceptional 

 species of Narcissus and Crocus may send up flower-shoots in Autumn months 

 (cf. Saffron Crocus). 



Cf. also Onion bulb, with reserves as glucose and mucilage, no flower. Tulip 

 (bulb), Anemone (Rhizome), Polygonatum (Rhizome) all storing starch. 



Perennation structures of root-origin as Tuberous Hoots : cf. Ficaria, swollen 

 segments, J in. long, storing starch, as extension of Buttercup root : Dahlia, large 

 * tuber '-growths, 6 in., store inulin. Orchis sp. swollen roots ; but greenhouse Orchids 

 commonly perennate as ' Pseudo-bulbs ', of swollen stem-internodes with remains of 

 foliage-leaves or scales. 



The limiting case of perennation is that in which all somatic structures die and 

 vanish at the approach of winter, leaving the race only in the form of seeds, as the 

 Annual plant ; such perennation may be made effective in these latitudes as the 

 result of frost (Reseda, Phaseolus) ; or may be part of the specialized organization of 

 the plant, as a consequence of exhaustion in seed-production (Helianthus, Zea). 



Special interest attaches to the case of the Biennial herbaceous plant which 

 takes a second season to attain reproductive maturity, storing reserves in the first 

 season, in foliage-leaves (Cabbage), bulb-scales (Onion), root (Beet, Carrot, Parsnip), 

 or hypocotyl (Turnip), to be exploited as food-crops for animal organism. 



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