I'KKSIDKNTIAL AOnRESS SECTION C. ' 71 



t^actcrium campcstrc, from samples of imported seed obtained 

 by local tirms (i6), and distributed by them through the 

 country ; and Smith states ( 52 ) that there is good reason to 

 believe that both the black rot of cabbage and Stewart's disease 

 of sweet corn have been disseminated broadcast in the United 

 States bv ignorant and unscrupulous seedsmen. Both diseases 

 are transmitted to seedling plants from the seed. The angular 

 leaf spot (if cucumber caused by Bacterium lachrymans Smith 

 and Bryan (54) has also been shown to overwinter with the seed 

 and cause seedling infection, and epiphytotics of the disease may 

 result from the introduction into the fields of contaminated seed. 



In each case quoted above, the organism is carried on the 

 surface of the seed-coat, and the internal tissues of the seed are 

 itot actually attacked by the organism ; such contamination can 

 easily be removed by disinfection of the seed before plantiiig, but 

 there are other organisms which penetrate the seed coat and 

 attack the embryo. Cotyledonary infection is common in the case 

 of bean plants attacked by Bacterium pha^eoli, and seed produced 

 locally often shows a high percentage of infection. 



A particularly interesting type of cotyledonary infection has 

 recently been described in the case of a bacterial disease of 

 Pisum sativum (13). Externally the seed appears sound, and 

 shows no indication of infection, but the organism is frequently 

 present in large numbers in the tissues of the cotyledon, and 

 sometimes in other parts of the embryo ; a discoloured area in 

 the centre of each cotyledon is typical of this disease. Infected 

 seeds often fail to germinate, or in less severe cases the shoot is 

 abortive, brown, and dead at the tip, and laterals grow out 

 prematurely to take the place of the main shoot. Sometimes 

 brown streaks are to be seen on the youngest shoots, but other- 

 wise there is no further sign of disease until the flowering 

 period. The organism passes up the stem of the plant in the 

 motile stage, and is to be found in the seed and seed-pod. Very 

 few cases are known of an internal infection of the embryo such 

 as that described above. Bacteria are reported to occur sym'bi- 

 oticallv inside seeds of Ardisia crista (36). In this plant the 

 bacteria occur in nodules or pockets inside the seed between the 

 embrvo and the endosperm. Miehe considers this a case of strict 

 symbiosis. Instances of seed infection similar to that of B. 

 scminum are known in the fungi, e.g., in the case of the barley 

 smut (7), (Ustilago hordei iiuda), mycelium is found both in 

 the endosperm and the embrvo of the resting seed, and the 

 funeus during the early stages of the plant growth, grows up 

 with it in a state oi semi-synibiosis, without causing anv very 

 marked disturbance, until the flower spike begins to develop. 



Instances of seed coat infection and infection of ovarial 

 tissues by fungi are not uncommon ; in the mycorhiza-bearing 

 plants (43). the mycelium of the svnibiotic fungus of the 

 Ericacece was found to be present in the seed coat, but not in 

 the internal tissues of the seed. 



