176 American Horticultural Society. 



In the animal., the nutrient fluid of the body circulates through a definite 

 system of channels, being distributed from a fixed center to which it after- 

 Tvards returns from most intimate contact with the most remote parts. In 

 its circulation it serves both. as the medium through which nutriment is con- 

 veyed to the growing parts and effete matter is returned for expulsion from 

 the system. It therefore serves as a most direct and favorable channel 

 through which disease may be rapidly and effectively distributed to all parts 

 of the body, and suggests a similar distribution in plants. But here analogy 

 fails us. In the plant there is no definite system of channels through which 

 the fluids flow and return, neither is there a fixed center of distribution 

 As the food elements are absorbed from the soil, in water}^ soUition, the 

 crude sap passes upward through the various tissues, cells, and even cell- 

 walls, in accordance with the law of osmosis, until it reaches the leaves, 

 where, under the influence of Hght and chlorophyl, its chemical composi- 

 tion is changed, and it then passes to the various growing parts by the same 

 physical laws of distribution. It therefore becomes obvious that anything 

 of the nature of pathogenic germs could not be thus distributed on account 

 of the physical obstacles opposed, and if disease does become distributed 

 through the agency of the sap, it must be through abnormal chemical con- 

 stitution of the latter, which directly aflects and influences the various de- 

 pendent physiological processes, and thus the disease becomes one of nutri- 

 tion. 



One other very important means of distribution requires examination. 

 All the processes of growth, all the characteristics of the plant and its power 

 to respond to external influences, are centered in the protoplasm to so high 

 a degree that it alone, physiologically, is the cell upon which all else depends. 

 Whatever operates to disturb the functional activity of the plant, must oper- 

 ate through its component cells; and the degree to which the organism is 

 involved will depend upon the number of cells acted upon by the disturbing 

 influence. But when there is an impenetrable cell-wall, and the disease is 

 not one of nutrition, but arises from the action of some pathogenic germ, 

 how may one cell succumb to the influence of those in its vicinity? During 

 his examination of the endosperm cells of certain seeds, in 1881, Dr. Pangl 

 determined the presence of a system of channels in the walls, through which 

 a continuity of the protoplasmic masses in adjoining cells was established. 

 About the same time, Strasburger, Fromman,and others, determined a simi- 

 lar continuity in other plants ; and from that time on to the present a very 

 large number of confirmatory facts have been obtained, especially by Gardi- 

 ner, within the last two years. They are of such a nature as not only to 

 establish the law of continuity of protoplasm, but render it highly probable 

 that it is applicable to all living vegetable tissues ;* so that, as Sachs expresses 



■»Bot. Centralbl., XIV, 1883, pp. 89 and 121; Proc. R. Soc, XXXV, 1883, p. 

 163; Ibid., XXXIV, 1882, p. 272; Quart. Jrl. Mic. Sc, Ot-t., 1882; Jahrb. Wiss. 

 Bot., XII, 1880, p. 170. 



