. Carnegie Institution of Washington publication. 192 BACTERIA IN RELATION TO PLANT DISEASES. tubers resists well and appears to be but slowly acted upon by this organism (figs. 104, 105, 106). In young tubers, however, such as that one shown in figs. 83, 107, 108, there may be considerable areas of the starch-bearing tissue in which no starch occurs. These are most extensive on that side of the tuber longest occupied by the bacteria, and the only explanations which seem to fit the case are that (1) the potato plant has withdrawn the starch preparatory to the formation of a cork-barrier as App
. Carnegie Institution of Washington publication. 192 BACTERIA IN RELATION TO PLANT DISEASES. tubers resists well and appears to be but slowly acted upon by this organism (figs. 104, 105, 106). In young tubers, however, such as that one shown in figs. 83, 107, 108, there may be considerable areas of the starch-bearing tissue in which no starch occurs. These are most extensive on that side of the tuber longest occupied by the bacteria, and the only explanations which seem to fit the case are that (1) the potato plant has withdrawn the starch preparatory to the formation of a cork-barrier as Appel has described for B. phytoph- thorus in potato, or that (2) excreted products of the bacteria (enzymes or other sub- stances) have killed these cells or have so paralyzed their activities that the plant has not been able to make use of them for the storage of starch. A very little is sometimes found (figs. 105, 106). That the starch was once stored and then dissolved by diastasic action of the bacteria is contrary to all that we know of its behavior, both in vitro and in older tubers. In the inoculated plants of the Jamestown weed (fig. 88), of the black nightshade (fig. 91), and Physalis philadelphica (fig. 94), there was the same enormous multiplication of the bacteria in the vascular system, even at long distances from the point of inoculation, and the tissues were destroyed in the same way, with the formation of extensive bacterial cavities. Several observers have reported finding an excess of crystal-sand in plants at- tacked by this organism. This substance occupies particular cells and consists of numerous discrete tetrahedral crystals of calcium oxalate (fig. 88). It occurs naturally in a large part of the Solanaceae, the amount varying with particu- lar organs and with the age of the parts; it is, therefore, not easy to determine whether there is an excess of it in dis- eased tissues, but there seems to be. In most of the draw- ings crystal-cells are depicted diagra
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