UKMAllKAliLE I'KOPEUTIES OF ROOTS. 767 



the parench^'ma lying iinmeJiately below the epidermis, so that this again does not 

 furnish a universal distinction. 



But although all those characters, which have been used in turn to cliaracterize 

 the root, cannot be thus employed because they have not a universal value, yet one 

 distinguishing feature always remains, viz. that leaves are never produced from 

 root-tissues, and the greatest stress is to be laid on this point. After weighing 

 everything carefully we come to the conclusion that the plant, and even its 

 youngest developmental stage, the embryo, begins with a stem, which develops 

 leaves and roots. Stems, leaves, and roots may perform widely different functions, 

 may shape themselves accordingly, and may be metamorphosed into widely differ- 

 ent organs. A plant is comparable to a crustacean which is divided into a body 

 and appendages. The appendages in most cases serve as organs for locomotion, 

 grasping, and clinging, but are sometimes also metamorphosed into respiratory 

 organs, egg-carriei-s, Szc. 



EEMARKABLE PROPERTIES OF ROOTS. 



The small stem-structures which proceed from germinating orchid-seeds behave 

 very differently according to the nature of their germinating bed. From the small 

 tubercles of species growing as epipliytes on the bark of trees arise, first of 

 all, hair-like absorbent cells which adhere to the substratum; then roots make 

 their appearance, which also unite firmly with the bark, though their superficial 

 cells are not able to penetrate into it. The small tubercles of the tei-restrial 

 orchids, which inhabit the meadows and the humus of the forest soil; develop 

 roots which gi-ow down into the ground and direct their growing tips towards the 

 centre of the earth. In this way they di-aw the stem-structure from which they 

 originate down with them, and thus the tuberous stem in two years' time comes 

 to lie 6-10 cm. below that point in the meadow where the seed actually germinated. 

 The same thing happens with the embryos of many biennial and perennial plants, 

 especially of those whose underground roots and stems are subsequently used as 

 storehouses for reserve materials, e.g. in Carrots, Evening Primroses, in the Monks- 

 hood, Meadow Clover, Vincetoxicum, Dog's Mercury, Martagon Lily, Bulbous 

 Crowfoot {Davbcus, (Enothera, Aconitum, Trifolium pratense, Cynanch-um Vince- 

 toxicum, Mercurialis perennis, Lilium, Martagon, Ranunculus bulbosus), and 

 many others. In these plants also the embryonic stem is drawn more or less 

 deeply under the ground, and the scarred point of insertion of the cotyledons is 

 not infrequently found to be several centimetres lower down that it was at the 

 time of their withdrawal from the integument of the seed. 



Many roots arising later on from procumbent and from erect or twining and 

 climbing leafy stems have the power of exercising a pull on their stem. The roots 

 springing from the stem nodes of runners, e.g. from those of strawberry plants, 

 draw the nodes a centimetre below the ground. This is also the case with the 

 long roots proceeding from the stems of perennial primulas. When these primulas 



