. Canadian journal of agricultural science. Agricultural Institute of Canada; Agriculture. January, 1922. SCIENTIFIC AGRICULTURE. 165 and the protuberance on the tuber. In root and stolon galls tiie parasite event- ually reaches the phloem in which most of the food manufactured is conducted and in this tissue most of the hypertrophy^ occurs. The tuber is somewhat modified because of its function as a large storage organ and the plasniodia do not, as a rule, reach the i)hl()em but attack cells of the hypo- ilermis and cortex. Where a cell is covered by a Plasmodium, or part of one, the wall swe
. Canadian journal of agricultural science. Agricultural Institute of Canada; Agriculture. January, 1922. SCIENTIFIC AGRICULTURE. 165 and the protuberance on the tuber. In root and stolon galls tiie parasite event- ually reaches the phloem in which most of the food manufactured is conducted and in this tissue most of the hypertrophy^ occurs. The tuber is somewhat modified because of its function as a large storage organ and the plasniodia do not, as a rule, reach the i)hl()em but attack cells of the hypo- ilermis and cortex. Where a cell is covered by a Plasmodium, or part of one, the wall swells and softens. That it is changed chemically is shown by the modified staining. Through the soft- ened wall the Plasmodium penetrates by. Figure 8. — Black-stem of potato. Note the blackened tissues at A and also the rolling of the leaves. (After Coons, Mich. Bull. 85; Fig. 9 also.) protoplasmic protrusions which Kunkel calls ''infecting pseudopodia". Once in- side the ceil the, naked protoplasm of the myxomyce^e penetrates the limiting mem- brane of the host protoplast, and the two protoplasms are to an extent miscible. It is when the cell is thus infected that hyper- trophy begins. As the vegeta'^ive growth of the potato gradually ceases and matura- tion commences the spores of Spongospora subterranea are formed and these spores are aggregated into round masses known as spore balls. Such groups of spores are highly resistant to adverse conditions and are known to be able to live over in the soil at least three years. Before leaving this discussion mention should be made of dry rots following 8. subtenanea. If, in the development of the pustule, it happens that the cork layer which cuts off the parasite is not laid down, drying-out or dessieation follows in storage. The severity of this depends up- on the number'of pustules on the surface of the tubers which are not limited by a cork layer. It often happens that the spore balls are still present in the pustule in stor
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