THE VEGETABLE CELL. 63 



part after another grows old and dies ; new, active individuals 

 sprout annually from the old ones, and there is no natural termi- 

 nation to the life of the whole. At the same time, the possibility 

 is given for a plant, in consequence of this unceasing production 

 of shoots, to become separated into an unlimited number of dis- 

 tinct plants, in a natural way by spontaneous, or by artificial, divi- 

 sion. From this peculiarity of the unlimited growth of a shoot 

 has the German language derived the expressive terms gewachs 

 (a vegetable, from wachsen to grow). 



Observ. The peculiarity of their organization, and the unlimited power 

 of growth of plants, offer many difficulties to the definition of the Jiu-a- 

 tion of plants, and have given rise to many incorrect theories. Every 

 individual cell, and every individual organ has a determinate end to its 

 life, but the entire plant has not, since the individual shoots run through 

 theh^ periods of development quite independentily, and only share in the 

 weakness of age of the older organs when these are no longer able to 

 convey to the young shoots the needM amount of nourishment, in which 

 case the latter do not die from deficiency of vital energy, but are starved. 

 It therefore depends wholly upon the mode of growth of a plant whether 

 this occurs or not. When a plant possesses a thallus spreadmg horizon- 

 tally by the growth of its circumference, it can annually extend itself 

 into a larger circle, after the old parts in the centre have been long de- 

 cayed, as is seen in old specimens of crustaceous Lichens, in the fahy 

 rings caused by Fungi, &c. In like manner when a higher plant has a 

 creeping stem, and possesses the power of sending out lateral roots near 

 the vegetating points, and in this way conveys nourishment directly to 

 the young terminal shoots, the latter are wholly independent of the death 

 of the older parts of the stem and of the primary roots, and there exists 

 no internal cause for death in such a plant. It is truly a different plant 

 every new year and vegetates in a new place, but there is no definite 

 boundary between it and its predecessors j such a plant is like a wave 

 rollmg over the surface of a sheet of water, it is every moment another, 

 and yet always the same. Thousands of inconspicuous plants, of Mosses, 

 Grasses, Hushes, &c., have vegetated hi this maimer upon peat bogs and 

 similar localities perhaps for thousands of years. Plants with upright 

 stems are placed in much more unfavourable circumstances. It has been 

 declared of these also, and particularly of the Dicotyledonous trees (Be 

 Candolle, " PJiysiologie Vegetate^ ii. 984), that they have no internal cause 

 for death, but I behove incorrectly. Examples of very old trees, such as 

 De OandoUe collected (e. ^., Taxus 3000, Adansonia 5000, Taxodmm 

 6000 years old, &c.), only prove, naturally, tliat death occurs at a very 

 late period in many plants placed in favourable circumstances, but not 

 that it does not necessarily happen. To me there appears to exist in all 

 trees, whether they belong to the Dicotyledons, or, hke the Palms, to the 

 Monocotyledons, an internal cause which must produce death in time — 

 namely, the increasing difficulty of conveying the necessary quantity of 

 nourishment to the vegetating point, resulting from the elongation of the 

 trunk from year to year. Even when the force which carries the sap up 

 suffices to raise it to 200 feet or more (many Palms, as Geroxylon cmdieola^ 

 Areca ohrmea^ ^ttdiksx a height of 150 — 180 feet; some Goniferse, 6, ^., 



