SCIENCE. 



29 



action of one part with another, so common in animal 

 bodies, is almost or entirely wanting in plants, due prob- 

 ably to the absence of a well developed nervous system. 

 Nothing is more common than to find a leaf dotted here 

 and there with diseased parts, while the intervening tis- 

 sues remain active and healthy. No organ suffers be- 

 cause another is affected, unless there is a direct depend- 

 ence in the way of food supply or other similar reason. 

 Hence diseased action can not be rapidly communicated 

 from part to part. The tree never becomes flushed with 

 fever because some one or more of its members have 

 met with disaster. In order that disease may spread at 

 all, it is necessary that the disease producing agent shall 

 itself spread from its original point of attack. 



INHERITANCE, OR CONTINUANCE OF PECULIAR EF- 

 FECTS. 



The protoplasm of the cells is " the physical basis of 

 life" in plants. From this flows the issues of life. Not 

 only all other material products are secreted by the more 

 or less plastic, often semifluid, substance known by this 

 name, but the peculiar and unexplained products of 

 vitality are due to the same source. Whatever potential 

 difference exists in the seed of a thistle separating it from 

 that of a turnip ; in a bit of a twig of a Bartlett pear, 

 used as a scion, from the worthless stock on which it is 

 set ; whatever difference there may be between health 

 and disease, considered as a constitutional affectation, 

 resides in this wonderful, ever-present, ever-important 

 constituent of living plants — protoplasm. 



There is nothing more wonderful in the phenomena of 

 plant life than the peculiar tenacity with which an im- 

 pression once made is held by living protoplasm. We may 

 not be able, with all our skill, to introduce or cause a 

 change to take place ; but when an effect is produced, the 

 changed cell may by reproduction become tens of thous- 

 ands of similar cells, all having the same peculiarity of 

 vital potency and power. It is upon this principle that 

 horticulturists depend in the propagation of special vari- 

 ties of plants by grafting, budding, cuttings, etc. It is be- 

 cause of this mysterious but interesting quality of the 

 " germinal matter " of the tissues of plants that Baldwins 

 among apples, Bartletts among pears, Marechal Niel's 

 among roses, etc., are possible. 



Now any deviation from the normal character of the 

 plant by which it is rendered less capable of succeeding in 

 the struggle for existence on its own account, and by its 

 own forces must be considered a disease. Usually our 

 highly prized fruits are produced as abnormal growths, 

 and the trees that produce them are notoriously liable to 

 seriously suffer from enemies and unfavorable surround- 

 ings and conditions, which, to their rough, hardy progeni- 

 tors would have been as the summer shower and the 

 smiling sun. 



So the blotched leaves and variously colored foliage of 

 many decorative pets of the garden, are but indications 

 of a protoplasmic impression continuing itself as a disease. 

 When it happens that these disease changes of the plant 

 are beneficial to us, or when they in any way please our 

 fancy, we do not think of them as pathological conditions 

 and effects ; but when through the operations of the same 

 law the opposite is true, we quickly enough talk of failure 

 through disease. Our potatoes all go to vines with no 

 tubers, our strawberries blossom profusely but the 

 flowers are " blasted," our sweet corn becomes too big and 

 coarse, our melons lose their sugar, etc. How the impres- 

 sions originally occur we do not usually know, but that they 

 are made we cannot doubt, nor too clearly see their per- 

 manence, if we would study the causes of health and dis- 

 ease, and try to learn how to profit thereby. 



Connected with this topic is a most peculiar phe- 

 nomenon not yet well understood on the botanical side and 

 perhaps not yet adequately studied. Who can explain 

 why it is that a certain and regular abnormal growth 

 takes place on a given plant after the sting of a certain in- 



sect forming what is called a gall ? Anyone who has seen 

 the leaves of a jack oak ornamented with " oak apples," 

 especially if he has broken them open and examined the 

 complexity and regularity of their structure, can hardly 

 have helped wondering at the peculiar something which 

 could produce in an abnormal, diseased growth so close 

 an imitation of a true and proper fruit. What can be 

 more strange with- our knowledge of the constancy of 

 form and character in plant growth generally, than that a 

 tiny wound with the injection perhaps of a minute drop of 

 a special kind of poison by a particular insect, should 

 entirely modify this growth and produce, not a distorted, 

 irregular knot, but an uniform, constant and thoroughly 

 characteristic though abnormal multiplication and shaping 

 of cells, producing thereby an organic structure so pecu- 

 liar and so uniformly the same that it may be subjected 

 to all the procedures of natural classification and of 

 specific identification ! Though the subject has not been 

 studied from the botanist's stand-point, especially in its 

 physiological or pathological bearings as its importance 

 would seem to justify and demand, it is at least question- 

 able whether the microscope would reveal anything tend- 

 ing to explain the marvelous result. The structure is, like 

 other plant tissues, formed of cells which through inherent 

 forces and properties, rather than through external agen- 

 cies, shape themselves, and by their co-ordinated and 

 united impulses give form and character to the resulting 

 production. It is also here as elsewhere, the living proto- 

 plasm that receives and bears the directing impulse. The 

 cell walls passively bend and swell under its silent and in- 

 comprehensible, but dominating power. The wonder is 

 increased when we remember that the growth is not a 

 continued reproduction of the same thing, but that cer- 

 tain cells of the new structure are shaped and modified to 

 form the external wall with its various and inter-differen- 

 tiated layers, others to form the core or nucleus and still 

 others widely differing from any of the former to make up 

 the mediary parts of the gall. What subtle influence, 

 what magic power is it, that thus toys with the vital- 

 ized forces and substances of the plant ? What invisible 

 barrier turns the usually inflexible current of life from its 

 healthful and appropriate course and converts the onward 

 rush into swelling pools with their own peculiar currents 

 and eddies and waves, and self-controlled depths and 

 boundaries? A gall produced by a plant in obedience to 

 a particular act of an insect is certainly a most remark- 

 able thing, and merits the closest and most profound 

 study. Why should not man be able to effect as great a 

 modification in the growth of a tender plant, as a buzz- 

 ing insect ? If we knew how why should we not gather 

 grapes from thorns and figs from thistles? 



But we must not lose sight of the fact that so far as 

 the plant is concerned, a gall is a disease and sometimes 

 a very serious one. If there is anything whatever, in 

 plant pathology to support Dr. Lionel Beale's theory of 

 " disease germs" being the degraded but still living cells 

 of the ordinary tissues, it is this of insect galls. Is it not 

 possible that a careful study of the latter might be of ser- 

 vice to the specialist in gaining more and better knowl- 

 edge of the origin and development of cancer in the hu- 

 man body? 



PLANT DISEASES ARE DUE TO SPECIFIC AGENCIES. 



There is no more important item of knowledge con- 

 nected with vegetable pathology than that each disease 

 has its own predisposing cause, or, in other words, that 

 each disease is a specific thing itself, in the same sense 

 and manner as a particular plant belongs to a species 

 bearing relations to, but unlike every other species. 



There is no clearer illustration of the truth of the fore- 

 going than in the matter just before us of insect galls. 

 Entomologists have given these structures much atten- 

 tion, and it is found as easy to recognize the gall as a 

 species, as it is the insect that causes the growth. A skill- 

 ful specialist in this matter will give us the name of the 



