164 CEOWN-GALL OF PLANTS. 



Whether this suggested mechanism of distribution actually occurs in 

 the crown-gall must be left for further study. Owing to the absence 

 of visible channels of infection and to the difficulty of staining the 

 schizomycete in situ, we do not know where nor to what extent it 

 occurs in a dormant condition outside of the tumor proper; but in a 

 very interesting and destructive fungous gall of ^Vest Indian lime 

 trees, studied in the Laboratory of Plant Pathology for several years, 

 Miss Florence Hedges has demonstrated that the fungus may grow 

 through the stems to a distance of several feet from the primary 

 tumor before an internal secondary tumor develops. The distance 

 in one case was so great that the writer of this paragraph supposed 

 it to be a second external infection until proof to the contrary was 

 obtained by tracing the internal mycelium through the wood from 

 the primary to the secondary tumor. Here the bulk of the abnormal 

 growth consists of wood. A bulletin on this subject is in prepara- 

 tion. 



It is probable that the parasite in its migrations from one part of 

 the plant to another does not make free use either of the vessels or 

 of the intercellular spaces, at least we have not been able to find it in 

 them. Rather we think it is imprisoned Vvdthin the specially stimu- 

 lated and rapidly dividing cells and is by the growth of these cells 

 carried along. The location of the visible metastasis would then 

 depend on where the most favorable conditions for rapid growth 

 developed. There would then be a slight chain of morbid cells all 

 the way from the primary tumor to the secondary one. Further 

 studies are necessary. 



Plate XXX shows a photomicrograph made through a young 

 metastatic tumor in the petiole of a daisy leaf. The whole interior 

 is a mass of rapidly proliferating morbid tissue (parenchyma cells 

 and distorted bundles), but it has not yet ruptured to the surface, 

 the outermost tissues being the normal tissues of the leaf stalk. 

 Later such a tumor would tear apart these tissues and appear on 

 the surface. The primary tumor in this case was some months older 

 and situated lower down on the stem. There are some indications 

 in this section that tumor cells are growing between and wedging 

 apart larger normal parenchyma cells (infiltration?), and this phe- 

 nomenon may be seen conspicuously in the section shown in 

 Plate XXVII* 



A third likeness which seems to us of some importance is the fact 

 that a certain degree of immunity can be induced in the plants by 

 repeated inoculations. When several inoculations have led to the 

 formation of successive galls, it is then usually impossible to induce 

 galls in the affected daisies by inoculating again with pure cultures of 

 the same strain which produced the initial tumors. One set of 



213 



