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THE TROPldAL AGRICULTURIST 3 . [November i, 1884 



In closing this article, we cannot help congratulating 

 ourselves and the colony on the possession of so valuable 

 an institution as are the Brisbane Botanic Gardens. The 

 good effected by it is silent and unobserved. But it is 

 none the less wide-spreading and pemanent. Nor c;iu we 

 withhold our need of praise from the head gardener. Mr. 

 1'ink is evidently the right man in the right place. We 

 had in Mr. Walter Hill a faithful, indefatigable and highly 

 intelligent public servant. It is very pleasant to know that 

 in his successor we have all these quali.ies still embodied, 

 together with much of that increased knowledge which 

 every succeeding generation is able to attain. In all matters 

 appertaining to his profession Mr. Pink is abreast of the 

 age, and is certainly the right man in the right place. — 

 Planter and Farmer. 



THE DEATH OF PLANTS. 



Life is one continual series of changes — 



" By ceaseless action all that is subsists.*' 

 The result of these changes is gain or loss, , waste or 

 repair, now one, now the other; or occasionally (and in- 

 deed generally) both simultaneously. While a proper 

 balance and equitable adjustment between gain and loss 

 exists, the plant lives and is healthy. Directly the balance 

 is disturbed the plant may live indeed, but it becomes un- 

 healthy; and if the disturbance continue — if waste over- 

 take repair — if nutrition be persistently impaired, still mere 

 if it be arrested, the plant inevitably dies. This is that 

 gradual and slow, but sure march of destiny, which comes 

 sooner or later to all living things at their appointed time. 

 That time comes when the tissues are — from that degener- 

 ation of their substance which may be a morbid process 

 resulting from injury, or which may be merely the necessary 

 result of the growth and maturation of the plant, or from 

 the failure of supplies — no longer able to carry on their 

 life-work. The period in question varies as to its occur- 

 rence. A "Wheat plant uses up its life within a few months, 

 an Oak tree within a few centuries, and there is every 

 intermediate period. 



But, in addition to changes which are the result of an 

 inevitable march of events, death in plants sometimes comes 

 suddenly from violence, life action is arrested in its full 

 flow and tide, and by much the same essential causes as 

 those which extinguish the life of animals. The death of 

 plants is the death of protoplasm. Prevent the access of oxy- 

 gen to the living cell, and the movements of the protoplasm 

 will be arrested and ultimately cease altogether. The pro- 

 perties and functions of protoplasm have already been 

 explained. It is their destruction and their cessation which 

 constitute death. But the death of a part is not necess- 

 arily the death of the whole, and the individual cells of 

 plants are, as a rule, much more independent one of the 

 other thau are the individual cells of an animal. A root, 

 or a leaf, or a mass of roots, and a number of leaves may 

 be injured, or even killed, and the plant will still live on, 

 because there are more left behind uninjured; and these, 

 relatively speaking, do not suffer from the damage done 

 to their fellows. A tree maybe stripped of its leaves and 

 may still live, because there are cells which are uninjured, 

 and which will do their parts towards compensating the 

 injury. A felled tree by the roadside will often be seen 

 pushing up new shoots in a manner that would be imposs- 

 ible in the case of an analogous injury done to one of the 

 higher animals. The lower the organism, the less special in 

 its conformation and construction, the more independent 

 are its constituent cells. The higher the organism, and the 

 more specialised its structure, the more dependent one upon 

 another are the structural elements of whichit is compounded. 

 Natural death may be described as an exhaustion of the 

 protoplasm — its water evaporates or is drafted elsewhere ; 

 and so with its soluble or liquid contents — the insoluble 

 and the useless remain behind. We see this in the case 

 of the leaves every autumn ; their protoplasm dries up, their 

 chlorophyll degenerates and disappears; they are emptied 

 of starch and other matters, which are conveyed to some 

 other part of the tree to be stored up for future use by 

 the new growths in the following season, till at length 

 nothing is left but a framework of dry cellulose, a quantity 

 of mineral or earthy matter, and such material as could 

 not be dissolved or transported. In other organs the con- ' 

 tiuuous maturing process at length results in the blocking | 

 up of the cells and tubes by continued deposit in the in- j 



terior. Osmosis can no longer go on between them, for 

 then- altered structure prevents it, aud in consequence the 

 protoplasm disappears. Just as in human beings, the 

 minute blood-vessels get " bony," or otherwise deteriorated 

 in structure, so do the cells and fibres of plants become 

 unfit to carry on the processes of life. 



For the purposes of the cultivator it is very desirable 

 that he give an eye to the way in. which plants die, and 

 to the causes which induce death. The subject may be 

 looked at from various points of view. From the structural 

 point of view death may begin in the cells of the root, 

 in those of the stem, in those of the intermediate "col- 

 lar," or in those of the leaves, and the appearances pre- 

 sented will be found to differ correspondingly. 



From a physiological point of view death may result 

 from starvation or from suffocation ; the process in each case 

 may be partial and gradual or immediate and complete. 

 Suddeu death, or death by violence, results from the in- 

 juries inflicted by too high or too low a temperature, 

 electric shocks, sunstroke, strong corrosives, and the like. 

 These destroy life by disorganising the protoplasm, break- 

 ing up the tissues, and arresting the natural movements, 

 and cause death by destroying the machinery or paralysing 

 its action. The gradual effects produced by such injurious 

 agencies as noxious vapours from kilns or factories, or as 

 insects, or parasitic fungi, are the same as those produced 

 by starvation or suffocation. In the neighbourhood of towns 

 it may happen that the relative absence of oxygen, or, 

 what comes to the same thing, the inability to use what 

 there is, may conduce to the death of plants quite as much 

 as the direct injury caused by noxious vapours. A perusal 

 of the foregoing chapters as to the food and growth of 

 plants will suffice to show why plants die; and a con- 

 sideration of their life-history as here set forth will show 

 how the cause that may kill at oue stage of active growth 

 may be all but harmless at another stage of growth. 



Death Beginning at the Root.— When death begins at 

 the root the supply of water, and of the air and food 

 derived from the soil, is cut off, and the plant ultimately 

 perishes of starvation. Death at the root may result from 

 injury inflicted by small parasitic worms, insects, rats, or 

 other creatures — from unsuitable conditions of soil, too 

 much or too little water, deficient drainage, deficient aer- 

 ation, or from the presence of really poisonous ingredients. 

 If the cause is widespread, so as to involve a majority or 

 the whole of the roots, the con-equences are proportion- 

 ately serious; if only a few are affected the plant may 

 not be visibly or materially injured. The effects will be 

 first and most especially obvious at the point of injury, 

 and at the growing points where the life-functions happen 

 to be going on most vigorously at the time. Thus, if the 

 young shoots and young leaves are in full activity at the 

 time when root-misehief occurs, they will the soonest show 

 the effect of cutting off supplies — they will wither and 

 droop. If the process is slow and gradual the leaves will 

 become emptied of their contents, their chlorophyll will 

 change colour, the plant will assume a sickly ye'low look 

 very characteristic to the practised eye. The older por- 

 tions of the plant, with their reserve stores of water aud 

 food, may not immediately suffer; and it is from them 

 that the materials requisite for any effort at repair and 

 reorganization must, if it be possible, be made. Thus a 

 plant may grow for some time after injury, and then 

 suddenly flag, because its reserve supplies are at length 

 exhausted. It follows from this that death from starv- 

 ation as a cousequence of root-mischief is not generally 

 a sudden, hut more often a gradual process, the length 

 of time of course varying according to the nature of the 

 mischief, and specially according to the nature and con- 

 dition of the plant. 



Death Beginning at the Leaf. — This may be appreci- 

 ated from what has been before said as to the functions 

 of the leaf. The leaf is an organ of nutrition, of respir- 

 ation, and transpiration; if its functions are sufficiently 

 interfered with, death will result either from inanition or 

 from suffocation, or from both combined. The power of 

 resistance that a leaf has may be inferred from its structure. 

 A thick fleshy leaf, with layer after layer of chlorophylt- 

 coutaimng cells, with relatively few pores and a thick 

 skin, is obviously better able to resist injurious agencirs 

 than a thin leaf whose delicate texture speedily withers 

 and falls a prey to adverse circumstances. 



