. A compendium of general botany. Plants. 140 COMPENDIUM OF GENERAL BOTANY. contact with water and particles of soil, to enable them to take np and conduct food-snbstances in solution. Other substances not soluble in water are rendered capable of being taken up by the root-hairs. Some mineral sub- stances are made soluble by a secretion of the root itself, perhaps an organic acid. According to Sachs, this may be demonstrated by means of a polished marble plate, osteolith- or dolomite-plate, upon which growing roots produce iigures of corrosion. Blue litmus paper is turned I'ed by this excretio
. A compendium of general botany. Plants. 140 COMPENDIUM OF GENERAL BOTANY. contact with water and particles of soil, to enable them to take np and conduct food-snbstances in solution. Other substances not soluble in water are rendered capable of being taken up by the root-hairs. Some mineral sub- stances are made soluble by a secretion of the root itself, perhaps an organic acid. According to Sachs, this may be demonstrated by means of a polished marble plate, osteolith- or dolomite-plate, upon which growing roots produce iigures of corrosion. Blue litmus paper is turned I'ed by this excretion of the roots. The activity of the root-liairs also reduces or entirely removes certain salts from the soil, as lime-salts, phosphates, and compounds of ammonia. Besides the organic acid referred to, roots also secrete CO^. In plants devoid of roots the solul)le food-sub- stances are taken up by the rhizoids^ hair-like structures met with among the prothallia of ferns, and among the lichens and mosses. In MarcJumtia these hair-like rhizoids possess peculiar elevated ^ thickenings of the cell-wall which project inward; young seedling they have perhaps a mechanical function, namelv, with particles of ^ " ^ n << ^i ^^ " soil adhering to to prevent collapse oi the cells, the root-hairs. B, The same with /7, i â in, soil-particles VO ^'mI hooU. washed away. (After saciis, from In the plants of moist warm climatesâa con- Frank.) . -/J ⢠11 1 1 ⢠dition artincially produced m our greenhousesâ roots very frequently develop from aerial organs. Such roots may subsequently enter the soil, in which case the subterranean portion performs the function of an ordinary root; or they may remain permanentl}' suspended in the air, in which case they are sj)ecially organized to serve as aerial organs (Aroidece, epii)hytic orchids). In the anatomy of true aerial roots there is found just outside the normal root-cortex a covering of several cell-layers in thickness called th
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectplants, bookyear1896
