63 



ESSENTIALS OF VEGETABLE PHARMACOGNOSY. 



tion into the mature condition of tbe plant, forms of structure here considered as ap- 



The phenomena of germination are not im- 

 portant from the standjKJint of pharma- 

 cognosy, and a mere outline of them is 

 here given. 



Animation is probably not entirely sus- 

 pended during the resting period of the 

 seed. That is, there is an apparent inter- 

 change of substance, due to vital action, 

 between the seed and the surrounding 

 atmosphere, although extremely slight, so 

 long as the former possesses its vitality. 

 Germination depends upon (1) a specific 

 temperature, varying for seeds of differ- 



plying to the root concern only flowering 

 plants and the very highest of the crypto- 

 gams, yet the description is applicable to 

 all roots used in medicine, 



STRUCTURE OF THE ROOT. 



Upon examining a transverse section of 

 the root in its rudimentary condition 

 (Fig. 352) it is possible to distinguish three 



bodies of tissue exhibiting characteristic 

 differences in their cellular elements. Th<> 

 central portion is orrnpiod by a solid 

 cylinder called the Plerom (a). Outside 

 of this there is a hollow cylinder called 



ent species and for those of the same the Periblem (b), and still outside of this 

 species when they have become habitu- and upon the surface of the root a second 

 ated to essentially different climatic con- hollow cylinder, the Dermatogen (c). The 



ditions; (2) a specific saturation, also vary- 

 ing with different seeds — that is, the ab- 

 sorption of an amount of water bearing: 



last mentioned develops a primary cover- 

 ing called the Epidermis. The epidermis 

 consists in its earliest stage, and there- 



a fixed ratio to the weight of the seed; fore at the very tip, of a number of lay- 



(3) a partially fixed degree of lip:ht exclu- 

 sion; (4) the presence of free oxygen. Un- 

 der these conditions ready prepared nutri- 

 ment is dissolved, other forms become 



ers of cells which protect the apical grow- 

 ing point of the root, and is therefore 

 called at that point the Root-cap, Tow- 

 ard the summit of the root-cap the outer 



digested by special vegetable ferments layers successively wear off or are cast 

 (Enzymes) present, heat is developed, cell off, so that the epidermis becomes reduced 

 propagation and cell growth take place to a single thickness of cells. Here it fre- 

 and the development and growth of a quently develops a dense covering of Hoot- 

 hairs which adhere tenaciously to the soil 

 and perform various processes connected 

 with absorption. For this reason the 

 epidermis of the root is known as the 



plant from the embryo commence. By 

 the growth of the embryo the radicle 

 is protruded through the micropyle, the 

 rest of the body soon following. The 



radicle, if it does not already point di- Piliferous Layer, Still further up these 



hairs have fallen away and the single 



rectly downward, turns in that direction 

 and develops into a root. The opposite 

 end of the embryo, if it does not already 

 point upward, turns in that direction and 



layer» after slight modifications, becomes 

 converted into the epidermis proper. This 

 has a variable duration in different plants 



develops as the apex of the stem. The and is consequently found covering the 

 stem above the cotyledons is called the root for a greater or less distance upward. 



Bpicotyl, that below them the Hypocotyl. 

 The cellular nature of development and 

 growth demands a general knowledge 

 of histology for their understanding, so 

 that we shall here consider, so far as pos- 

 sible, only the gross results of the proc- 

 esses, or such characters of the root and 

 stem as can be demonstrated by other 

 than histological methods. Such refer- 



Almost always its duration is very short. 

 It either disappears altogether, being re- 

 placed by a structure (Periderm) devel- 

 oped from the periblem, or in rare cases 

 itself develops into the periderm. 



The periblem of the root develops into 

 the Cortex, consisting of a number, often 

 a large number, of layers of cells. Its 

 outermost portion, usually of one layer of 



ences to cellular structure as are here cells, presents a different appearance from 

 necessary are given rather figuratively the subjacent layers, and is the Hypo- 

 than technically- The mode of growth 

 in root and stem, and the structures re- 



sulting, are sufficiently different to re- 

 quire separate treatment. Although the 



dermis (Fig. 354b), in the case of the root 

 becoming the Exodermis. The hypoderm 

 lies against the inner face of the epi- 



denn (a), while that neraista. hponraiTifir 



