92 



HISTORY OF THE VEGETABLE KINGDOM. 



pven. The endocarp is always perforated at the 

 interiml point of the pericarp, to which the tro- 

 phosperm is attached, because the sarcocarp, being 

 the only vascular part of the pericarp, and the 

 only one that can furnish the materials required 

 for the nutrition of the seed, it is necessary that 

 the endocarp should have an opening to allow a 

 passage to the vessels which go to that organ. 



The trophosperm sometimes bears only a single 

 seed, but at other times supports a great number. 

 Wlien its surface presents obvious prolongations, 

 each of which suppoits a seed, these prolonga- 

 tions are named podosperms; as, for example, in 

 the pea, and bladder campion. 



The trophosperm, or the podosperm, commonly 

 stop short around the hilum of the seed. When 

 they are prolonged beyond that point, so as to 

 cover the seed to a greater or less extent, the 

 prolongation takes the name of arillus. 



The arillus being merely an expansion of the 

 trophosperm, does not belong to the seed, as it is 

 generally said to do, but to the pericarp. 



The partitions are usually longitudinal, so as 

 to extend from the base to the top of the peri- 

 carpal cavity. In some very rare cases, as in 

 cassia, fistula, and a few other leguminosas, they 

 are transverse. These partitions are further dis- 

 tinguished into complete and incomplete. The 

 origin of the false partitions is exceedingly vari- 

 able. Sometimes they are formed by a more 

 or less considerable projection of the tropho- 

 sperm, as in the poppy : sometimes by a pro- 

 longation inwards of the edges of the pericarpal 

 valves, &c. 



The trophosperm is that pai-t of the pericarp 

 to which the seeds are attached. Sometimes it 

 presents at its surface a greater or less number 

 of small projecting mammillffi, each supporting 

 a single seed, and which are named podosperms. 



When a pericarp is multilocular, the tropho- 

 sperm generally occupies its centre, and is then 

 named central. In this case, it is formed by the 

 meeting and union of the partitions, and in the 

 internal angle of each cell presents a greater or 

 less projection. 



The arillus belongs essentially to the pericarp, 

 it being merely a prolongation of the tropho- 

 sperm. It is therefore incorrect to consider it, 

 as many botanists do, as forming part of the 

 seed, upon which it is merely applied, without 

 at all adhering to it, excepting around the hilum. 

 Few parts of plants exhibit so many varieties in 

 their form and nature as the arillus. It is con- 

 sequently very difficult to give a strict definition 

 of it, which may be applicable in every case. 



In the nutmeg (inj/ristica officinalis^, the arillus 

 forms a fleshy covering, of a light red colour, 

 divided into narrow and unequal shreds. This 

 is the part which is used in phai-macy, and is 

 known by the name of mace. Polygala vulgaris 

 lias a three-lobed ariUus of small size, fomiing a 



kind of little crown at the base of the seed. In 

 the common spindle-tree {euonymus europoeus), 

 and the broad-leaved species of the same genus 

 (euonymus latifoliv£), the ariUus, which is of 

 an orange colour, envelopes and conceals the seed 

 on all sides. In euonymus verriicosus, it forms 

 an irregular cup, which is open above. 



From the small number of examples given 

 above, it will be seen that the arillus varies ex- 

 ceedingly in colour as well as in fonn and con- 

 sistence; but, as its origin is the same in all 

 cases, it is easily distinguished, notwithstanding 

 the numerous forms under which it may present 

 itself. Various parts have often been taken for 

 arilli ; for example, the outer, obviously fleshy 

 part of the proper integument of the seed, in 

 the jasmine, the endocarp, as in the coffee 

 {coffcea arabica), the rutacese, &c. It is a gen- 

 eral law, to which no exception has yet been 

 found, that the arillus is never met with ui 

 plants which have a monopetalous corolla. The 

 taierncemontana might seem to form an excep- 

 tion; but, when better examined, its alleged 

 arillus is merely the outer part of the proper 

 integument of the seed, which is soft and fleshy. 



Having examined the component parts of the 

 pericarp, the partitions, the cells, the tropho- 

 sperm and the arillus, let us return to the pericarp 

 considered in a general point of view. 



In the pericarp, as in the ovary, there aa-e dis- 

 tinguished : 1st, The base, or the point by which 

 it is fixed to the receptacle or the peduncle ; 

 2dly, The summit, which is indicated by the 

 place formerly occupied by the style or the 

 sessile stigma ; 3dly, The axis. Sometimes the 

 axis is not merely imaginary, but has a real ex- 

 istence, and is named the columella. At other 

 times it is fictitious, or is represented by an 

 imaginary line, passing through the centre of 

 the pericarp, from its base to its summit. 



The columella foiTus a kind of little pillar, on 

 which are supported the different pieces of the 

 fruit, and which remains at the centre of the 

 pericarp, when these have fallen off; as in the 

 euphorbisE and umbelliferse. 



The seeds being enclosed in the pericai-p, it 

 becomes necessary, to allow them to issue at the 

 period of their maturity, that the pericarp should 

 open in some manner. The name of deht- 

 scence is given to the action by which a pericarp 

 naturally opens. There are pericarps, however, 

 which do not open, and which are temied inde- 

 hisccnt; as in the synantherea;, labiat«e, gra- 

 mines, &c. 



Among the pericarps which open naturally at 

 the period of maturity, there are distinguished : 

 1st, The 7-uptile pericarps, or those which burst 

 into irregular pieces, of which the number and 

 form are very variable ; 2dly, Those which open 

 only by holes formed at their upper part, as in 

 the germs a}itirrhinum ; odly, Those which open 



