May 8, 1889.] 



Garden and Forest. 



225 



hot, and buds oi Magnolia conspicua, wliich were completely 

 closed on the morning of that day, had, by the middle of the 

 afternoon, burst into fi.ill bloom. Tuesday night ice was 

 formed in tubs and pails more than half an inch thick. But, 

 strange to say, the Howers of none of the herbaceous or bulb- 

 ous plants have suffered. The liowers of the Forsythias, 

 almost fully expanded, of the Magnolias and of the Sweet 

 Almond are uninjured, while those of Rhododendron Early 

 Gem, growing in a low, damp situation, which were fully out 

 on Monday, were frozen stiff', and are, of course, entirely 

 ruined. 



Boston, April 24th. c. 



Principles of Physiological Botany, as Applied to 



Horticulture and Forestry. 



XIX. — D1STURB.A.NCE OF Function. CERrAiN Plant-Diseases. In- 

 juries AND THEIR REI'AIR. 



AS stated in a previous paper, the diseases of plants 

 belong to the province of vegetable pathology instead 

 of vegetable physiology, and they are referred to in this series 

 merely because we can sometimes learn something of the 

 functions of a healthy organ by watching its behavior when 

 it is affected by some disturbing cause. Even if we do not 

 know what the disturbing cause may happen to be (much less 

 remove it), we may still gain further insight into the action of 

 an organ or an organism which has come imder its inliuence. 



Before considering this subject, attention should first be 

 directed to what are called monstrosities. Everyone is famil- 

 iar with the commonest forms of monstrosities, such as four 

 and five-leaved Clover, consolidated shoots of Asparagus, 

 green Roses, and the like. These variations of number, of 

 union of parts, of accidental division, and changes in color, 

 throw much light on the laws which go\'ern structure, but diey 

 do not usually aid us in the examination of the office of organs 

 which are abnormally developed. There are, however, some 

 strange modifications of structure which follow the attacks of 

 insects, for instance, in the case of the so-called gall-insects. 

 The slight injury inliicted and the subsequent irritation caused 

 by these insects give rise to variously-shaped excrescences, 

 which are characterized in numerous instances by an increase 

 in the amount of astringent matters, tannin, gallic acid, and 

 the like, collected in the neighboring cells. In fact, as every- 

 one knows, the amount of such astringent matter in the galls 

 on a species of Oak is so great that they become a matter of 

 commercial importance. The symmetrical outgrowths on the 

 stems of some Willows are doubtless familiar to all. 



For an interesting account of the relations which exist be- 

 tween certain insects and enlarged organs of some species of 

 tropical plants, the reader is referred to the work mentioned 

 in the foot-note.* From Mr. Belt's statements it appears 

 that some of the Acacias of Nicaragua have enlarged appen- 

 dages (stipules) at the bases of their leaves, which secrete 

 large amoinits of saccharine matter for the nourishment of 

 ants. The insects are completely satisfied with this store of 

 food which is provided by the plant, and they do not attack the 

 leaves. These ants serve as a well-fed garrison to defend the 

 plant from the attacks of leaf-cutting ants. Other cases quite 

 as remarkable as this have been noted in the tropics. In all of 

 them some organ is excited to the exercise of a function not 

 commonly associated with it. But such cases are to be re- 

 garded as modifications which have probably arisen by slow 

 adaptations through a series of generations, and hence are not 

 to be properly regarded as disturbances of function. 



Certain fungi, notably the so-called rusts, smuts and mildews, 

 are exceedingly destructive to the cells and contents of cells of 

 many plants. Besides being destructive to the contents of 

 cells, certain fungi may give rise to extraordinary distortions 

 of form of the host-plant. Among such may be mentioned 

 the familiar cases of that which causes the outgrowths on our 

 common Cedar, and that which produces the diseased state of 

 the grain of Rye (known as "ergot"). But with these in- 

 vasions of fungi we are now to deal only in the most general 

 manner. 



For the purpose of our present examination, these fungi of 

 all grades may be regarded as parasitic, subsisting on living 

 tissues and their living contents. Many of them act also on 

 the same matters in dead plants, and some act only on non- 

 living matter, but the latter may now be left out of account. 

 A parasitic fungus is unable to utilize inorganic matter. It 

 must have organic matter in some form, and this it obtains 

 from the contents of the living cells of its victim. Throughout 

 the organism the threads of the fungus make their way, fre- 

 quently sending out invading filaments which grow l)ut a short 



* Belt's Naturalist in Nicaragua. 



distance from the path of the main threads. All of these are 

 engaged in consuming antl appropriating the organic matters 

 accumulated \t\ the iiost-phuit. In some cases, the bliglit 

 sweeps through a plant with great rapidity, while in others the 

 invasion is insidious, and the progress through the attacked 

 plant is, on the whole, rather gradual. In some manner, either 

 l)y separated cells formed after the manner of buds, or l)v what 

 are known as spores of sexual origin, these in\'ading ])lants are 

 disseminated in some instances with frightful rapidity. These 

 spores are frequently very much more resistant to destructive 

 agents than are the invading threads, and hence the problem 

 of destroying the fungus, as one might say, of an herl), " root, 

 and stem, and leaf , and seed," is very difficult and disheartening. 

 But the arduous labors of the cryptogamic botanists liave sug- 

 gested some efficient remedies for a very few cases, and others 

 will doubtless follow. To see what remedies against fungi can 

 Ije expected to accomplish, a few words must be devoted to the 

 conditions requisite to the growth of some of these fungi. 

 They require precisely the conditions necessary to the rapid 

 growth of vegetable cells in general, namely, moisture, food, 

 plenty of oxygen, and a certain temperature. 



When a fungus has fairly invaded the tissues of a plant, there 

 is very little hope of resisting its further advance. In a few in- 

 stances, experiments have shown that much may be done 

 towards warding off" invasion and preventing the fungus from 

 getting a foot-hold. Thus, the fungus which is known as the 

 " Downy Mildew " of the grape-vme, has been successfully 

 combatted in certain localities by the use of solutions of salts 

 of copper sprinkled at intervals on the leaves. But it should 

 be acknowledged that in some other instances the solutions 

 have failed. In a few cases, also, the same remedies have been 

 more or less efficacious when applied to the forming fruit of 

 the Grape threatened by the fungus which produces the so- 

 called " black rot." But it has been well said that the results in 

 these instances are conflicting, and cannot be regarded as con- 

 clusive.! 



In experiments in France, the solutions known as Bordeaux 

 viixtxire (consisting of six kilograms of sulphate of copper in 

 100 litres of water and eight kilograms of lime in thirty litres of 

 water) and Eaii celeste (consisting of one kilogram of sulphate 

 of copper and two litres of ammonia in 200 litres of water) have 

 given excellent results in diminishing the ravages of mildew. 



In some cases, such as that of the fungus causing the so- 

 called " black-knot " of Plums, the only treatment suggested 

 with confidence is the complete destruction of affected trees, 

 thus lessening the spread of the malady. 



Certain fungi are very destructive when they attack non- 

 living wood, causing rapid decay. These invasions are fre- 

 quent in the case of some of our cultivated trees, and forest 

 trees which have their wood exposed by injury. In not a few 

 cases the resinous matters which impregnate the wood or 

 which are poured out after a mechanical injury, exert a true 

 antiseptic and preservative power. As a general thing. Nature 

 heals all wounds where this is possible by the formation of the 

 tissue known as cork. Even when the leaves fall in autimin, it 

 can be seen that by an anticipatory development of cork at 

 the twig, the wound which would otherwise be an open one is 

 already, at the fall of the leaf, a healed scar. 

 Cambridj^e, Mass. George Liiicolii Goodale. 



Periodical Literature. 



Mr. Frederick Boyle is an English author and amateur cul- 

 tivator of Orchids, whose enthusiasm for the latter branch of 

 his activity expressed itself last winter in two charming arti- 

 cles in Longman s Magazine, which were duly noted in these 

 pages. Now he writes again on the same subject in the 

 March number of the same periodical, the title of his chapter 

 being " Cool Orchids." Nothing could be more desultory 

 than his treatment, or more lively than his style. He passes 

 at a bound from Orchids in their suburban glass-frames to 

 Orchids in their native habitats, and lays a tribute of glowing 

 words now on the far-off tomb of some fever-stricken collec- 

 tor and now on the head of some favorite Odontoglossum or 

 Cypripedium. But all his paragraphs are entertaining, and 

 some of them are instructive. His main object is to inipress 

 upon the impecunious amateur that Orchids of many sorts 

 are easily within his reach. " I should like," he says, " to 

 publish it in capitals — that nine in ten of those suburban 

 householders who read this paper may grow the loveliest of 

 Orchids if they can find courage to try ; " and then he explains 

 how little courage is really needed. " Tiie plain truth is that 

 no class of plants can be cultivated so easily, as none is so 



t Professor F. L. Scribner's Communication in Bulletin of tlie Commissioner of 

 Agriculture, i388. 



