Interspecific Transmission of Mosaic Diseases of Plants 9 



appreciable distortion. The contrast between these two mosaics of 

 tomato is much greater than would appear from an examination of Plate 

 I (4, 5, and 6). 



The mosaic on Martynia louisiana Mill, shows as a distinct mottling 

 affecting rather large, well-defined patches. 



Nicandra Physalodes (L.) Pers. is affected by two mosaics. Mosaic 

 B (Plate II, 8 and 11) produces a distinct mottling consisting of small 

 light areas in the darker leaf. Generally the leaves are not much dis- 

 torted but often they are somewhat smaller than those of healthy plants 

 and they are sometimes slightly cupped, the edges turning downward. 

 They may be slightly rugose. The flowers are not affected except that 

 they also may be smaller than normal. Mosaic H on N. Physalodes 

 (Plate II, 10) produces almost no mottling, but instead one finds a pro- 

 nounced and characteristic distortion. The leaves develop very irregular 

 lacerated margins and become more pointed. The veins are more promi- 

 nent and straighter, and branch in a peculiar manner. The flowers are 

 often much affected (Plate III). They are almost always smaller than 

 normal, the sepals often show the peculiarities of venation described for 

 the leaves, and the corolla is often divided. The divisions of the corolla 

 do not always correspond to the normal petal lobes, and may divide it 

 into two or three parts of unequal size. 



Three mosaics occur on Nicotiana glutinosa. Mosaic B (Plate IV, 

 17 and 19) causes a fine mottling consisting of light green islands with 

 darker green showing along the smaller veins. Usually the mottling is 

 not very striking under greenhouse conditions, but it may be so in the 

 field where the plants grow rapidly. Mosaic D (Plate IV, 16 and 20) 

 shows as a very faint spotting. There are generally only four or five of 

 these small spots on each leaf. They are usually not clearly outlined 

 and may be evident only by transmitted light. Mosaic H (Plate IV, 

 14 and 15) is extremely pronounced and distinct, in contrast to the other 

 mosaics occurring on this species. The affected leaves show large con- 

 trasted areas of yellowish green, and sometimes dark green blisters, as 

 in the case of the small leaf in Plate IV, 14. The leaves are generally 

 somewhat dwarfed and distorted, and sometimes they are much reduced. 

 The appearance of this mosaic is similar to that of the familiar mosaic 

 on tobacco. 



Mosaic A on Nicotiana rustica L. (Plate VI) has a striking and unusual 

 effect. The leaves generally turn yellow and then brown near each point 

 of inoculation. The leaves near the growing point then turn yellow, 

 growth ceases, and the terminal bud and the younger leaves die and shrivel 

 up, leaving only the stump and some of the older leaves green. On 

 splitting the stem, it is seen that necrotic spots occur in the interior. 



Mosaic A on Nicotiana Tabacum L. (the well-known tobacco mosaic) 

 is characterized by a distinct mottling consisting generally of rather 



