3Q 



SCIENCE. 



insect on seeing its domicile, as readily as upon seeing 

 the winged inhabitant itself. Each one of the hundreds 

 of these curious structures differs from every other one, 

 and owes its existence to a different agent from that of 

 any other one. There are a very few possible excep- 

 tions to this if we limit the difference in insects to specific 

 distinctions, for it is known that at least one species pro- 

 duces several kinds of galls on the same parts of the 

 same plant, while others make somewhat different galls 

 on different parts of a given plant, as in the case of the 

 devastating Phylloxera. But every one knows that the 

 individuals of a species vary much among themselves, so 

 that our rule should be strengthened rather than broken 

 by th^se apparent exceptions. There are at least one 

 hundred kinds of galls known upon oaks ; hence we may 

 say there are one hundred specific agents, each working 

 after its own fashion and producing its own peculiar re- 

 sults. 



Much might also be said of diseases of plants caused 

 by insects which do not form galls, illustrating the same 

 thing ; but these are passed without remark to save time 

 and room for those more particularly falling under my 

 own observation and the subjects of more personal in- 

 vestigation, viz : those caused by parasitic fungi. 



Though having had a very good chance to find out, I 

 do not know of a single flowering plant in our country 

 which is not more or less injuriously affected by one or 

 more fungi, living as parasites on, or in, its substance. 

 Sometimes numerous species dwell on (or in) one host 

 plant ; sometime the same parasite preys on many kinds ; 

 but very often a particular fungus is found only upon a 

 particular supporting plant. Nearly all of these myriads 

 of thieves are so small that they cannot be seen, certainly 

 are not usually seen by the unaided eye, except as they 

 occur in masses. Many are at times exceedingly destruc- 

 tive, as witness the wholesale rotting of potatoes during 

 certain seasons, while yet in the ground and attached to 

 the stems of the plants ; and the dreaded rust of wheat, 

 which apparently cuts off the farmer's returns for a year's 

 labor in a week or a day. We pay less attention to the 

 diseases and death of uncultivated plants, but these, too, 

 suffer as severely. I have observed great areas of thickly 

 springing smart weed (Polygonum Pennsylvanicum and 

 P. hydropiper) destroyed almost as effectually as by fire, 

 by a vegetable parasite (Helmin thosporium) whose corro- 

 sive action caused the leaves, long before frost in autumn, 

 and before the maturity of the plant, to shrivel and die, 

 after which the entire plants soon succumbed. 



Though these mischief-makers are usually invisible 

 to untrained and unaided eyes, their peculiar effects are 

 ordinarily recognizable at once, by an expert, even with- 

 out his magnifier. Each has its own characteristic in- 

 fluence upon the host — one causing yellowish spots on 

 the leaves, another a curled and distorted growth, an- 

 other little cracks on the stems, another swellings like 

 insect galls, etc., etc. A closer examination brings into 

 clearer relief the different injuries or modifications of 

 growth, caused by each different parasite. Each faded 

 spot, each tumid projection, each rupture of the epi- 

 dermis, each blister and canker, each puncture and cor- 

 rosion, has its own more or less clearly marked charac- 

 teristics ; and each parasite has, as well, its own patho- 

 logical influences and effects. The grapevine alone has 

 at least thirty species of parasite fungi peculiar to it and 

 all more or less injurious, while an entire book of some 

 hundred and fifty pages has been filled with generic 

 and specific descriptions of fungi, known to occur on the 

 cultivated vine. (Thiimen, Die Pilze des Weinstockes, 

 Wien, 1878.) The list of specific and separate causes of 

 disease in plants thus immeasurably exceeds that known 

 to the wisest practitioner of medicine for man, for the 

 illustration from the grapevine, though a strong example, 

 is not exceptional. Of fungi, as a class, there are many 

 more species growing in Illinois than there are flowering 

 plants, putting the native and introduced together, — at 



least double as many. Large numbers of these, how- 

 ever, never grow on living plants ; they are the scaven- 

 gers of the vegetable world. 



Two questions may now be raised. (1.) Are all these 

 fungous growths really divisible into good specific forms ? 

 in other words, can the term species be applied to these 

 various productions in the same sense as it is used for 

 the higher plants and animals? (2.) Do those kinds 

 known to inhabit living plants really cause disease, or 

 are they mere concomitants of pathological conditions, 

 due to other influences ? 



These questions are continually pressing for answer, 

 founded on careful observation and skillful investigation. 

 The first one has been, and must be, answered unhesi- 

 tatingly in the affirmative by every botanist who has 

 made, or may make, a special study of the plants. 

 There are curious alternations of generation, as among 

 the lower animals — a given species presenting itself un- 

 der two, three, or even four forms. There are also de- 

 viations from the recognized type, and modifications due 

 to circumstances and conditions; but it is doubtful 

 whether these fluctuations are greater than in the species 

 of higher and better known organisms. It does require, 

 perhaps, keener perceptions to distinguish allied species 

 than among those having greater differentiation of parts, 

 as root and stem and leaf and flower and fruit ; but 

 none of these affect the general question. We admit 

 the probability of evolution of species in the world, and 

 should be theoretically disposed to look for greater plas- 

 ticity in these low forms than in the higher; yet, except 

 in the particulars cited, observation does not apparently 

 support the deduction. I am sure that any botanist, 

 equally familiar with the two, will as positively recognize 

 Puccinia graminis, the rust, or, rather, one of the rusts 

 of wheat, as he will Triticum vulgare, though the 

 former is very variable for a fungus. The same may be 

 said for Usfilago maydis, the smut of corn, and Zea mays; 

 but, in this case, there seems to be no variableness nor 

 shadow of turning in the characteristics of the parasite. 

 Hundreds of even better illustrations might be given, all 

 conspiring to enforce the opinion upon the skeptical, that 

 these low, mostly microscopical plants, have specific dis- 

 tinctions as characteristic and rigid as those found among 

 the higher organized, if not more respectable and reputa- 

 ble members of the vegetable kingdom. It is yet to be 

 proved whether or not hybrids ever occur among the 

 fungi ; the very tact that none are positively known, or 

 even reported as suspected, helps to indicate the good- 

 ness of the species to botanical eyes. Still there is much 

 to be done in the way of experiment, by sowing spores 

 and watching the development of the plants, before much 

 confidence should be placed in the slight distinctions 

 now used in many cases for specific separation. 



Passing to our second question, a direct answer can- 

 not be given. In the interdependence and complexity of 

 relations existing among all living organisms, it is ex- 

 ceedingly difficult to pronounce upon the exact effect of 

 any one of them, considered in and of itself. Cold water 

 is not regarded as poisonous to man, yet individuals have 

 severely suffered, even died, from the effects of a reason- 

 able (so far as amount is concerned) draught. Arsenic 

 is poisonous, yet there are those who swallow what would 

 ordinarily be deadly doses, with impunity. Poisonous 

 doses of opium are merely nerve restorers to the habitual 

 eater of the drug. Shall we then say that water causes 

 death when taken to allay thirst, and arsenic and opium 

 are not poisonous ? Shall we not rather say that what- 

 ever proves seriously injurious to man in a normal con- 

 dition, under the usual circumstances of his life, is the 

 poisonous thing, and the one which causes death ; while 

 we assign the peculiar and abnormal condition as the 

 cause in other cases, — as the over-heating instead of the 

 water. 



Measured by this standard there are many parasitic 

 fungi which must always be acknowledged as a " cause " 



