152 The Ohio Naturalist. [Vol. XIII, No. 8, 



green regions seem slightly swollen, while the yellow areas apjjear 

 appreciably thinner. Many of the affected leaves become crinkled 

 or show an irregular growth; this is due to an uneven tissue ex- 

 pansion; the healthy green regions develo]) more rapidly than 

 the yellow areas, hence a warping or crinkling results. Woods 

 (1902) states that in very severe cases the entire plant may become 

 so defomied that it is almost unrecognizable. 



As the plant becomes older and the flower buds form, there 

 may appear "what is known as "mottle top," although the plant 

 may have remained perfectly healthy up till flowering time. Ac- 

 cording to Sturgis (1S99), weather conditions may bring on the 

 disease at this time and affected plants may recover if conditions 

 'become favorable again. He regards "mottle top" as a later 

 stage and milder form of calico; the typical mosaic appearing 

 only in the earlier stages of plant development. The writer has 

 occasionally encountered this in the field and from his observation 

 it does not seem serious, as it apparently involves only a few of 

 the uppermost leaves, which are always removed at topping 

 time. 



Tomato. — Where tomatoes are forced under glass, mosaic 

 disease is not uncommon and appearances similar to mosaic are 

 also found in the field. One of the first investigators to call 

 our attention to the mosaic disease on tomato was Sturgis (1899). 

 He cites a case where a field of tomatoes was overtaken I33' an 

 early frost and severely nipped. As a result of this artificial 

 pruning, the disease made its appearance. Woods (1902) pro- 

 duced the disease at will on tomato and poke weed by severely 

 pruning healthy plants. See his plates 2, 5 and 0. Tomato 

 chlorosis and its infectious properties are discussed by Clinton 

 (1908). Hunger (1905) seems to be the first foreign investigator 

 who worked with tomato mosaic. He confirmed Woods' (1902) 

 pruning results, having used plants grown from seed from various 

 countries. Westerdijk (1910) carried out extensive experiments 

 with tomato mosaic, which show the disease is inheritable. According 

 to her the disease is conspicuous on stalks and fruit as well as 

 leaves. She says that the stalks frequently show a spiral band of 

 yellow color. During the earlier .stages of fruit development, 

 while it is still green she says, that the yellow spots are easily 

 recognized, but as the fruit matures, the deep red masks them. 



The yellow areas on the leaves, as for tobacco, seem con- 

 fined more or less to the tissues between the main veins. The 

 dark green regions nearby seem to assume a rather "over healthy " 

 aspect. Here again, an unequal growth of tissues cause the leaf 

 to warp or curl. In severe ca.scs, descriptively termed, "fern 

 leaf" appears. Here the main veins are considerably hyper- 

 trophied, while the intennediatc tissues altogether fail of develop- 

 ment, giving the leaf a very striking dissected appearance. 



