1270 PLANT BREEDING 



II. — Diseases and Pests. — It cannot be said that there are any 

 really serious diseases of the tobacco plant in the Ivast of Java : 



There is some small amount of fungous disease [Phytophthora Nicotianae, 

 Bacillus Solanaceantm Erw. Sm., Cercospora Nicotianae Jill, and Evr.,etc.), 

 but it occurs quite sporadically. More dangerous are the numerous insects 

 {Heterodera, Grylhts, Gryllotalpa. the larvae of Plnsia, Heliothis, Prodenia, 

 Lita, and Opatrum). 



The larva of Lita solanella, particularly, produces galls in the young 

 plants which prevent normal growth. A rather serious disease is the myste- 

 rious " mosaic disease " which chiefly attacks fine-leaved races. In spite 

 of many studies, it is not yet known whether this is a fungus disease or results 

 from defective assimilation. vSuch defective assimilation certainly occurs, but 

 is it caused by bacteria or by the soil, moisture or heat ? This problem will 

 no doubt be better solved by laboratory experiments in which the external 

 conditions can be minutely regulated. In the open field there are many fac- 

 tors which escape investigation, in spite of the most estensive weather ob- 

 servations. The importance of the latter, however, cannot be over-estimated, 

 above all in the study of tobacco, and it is a great advantage to the 

 Station of Dj ember that it possesses a meteorological installation in the 

 vicinity of one of the experimental fields. 



III. — Mutations. — The Author next deals with some rather inter- 

 esting forms of mutation (or deemed to be such) : 



There is for instance a form with a double flower, very pretty, with the 

 outer corolla turned up, which has repeatedly been observed in Java. It 

 is extremely rare, but breeds true in all its characters ; one double plant 

 among the seed plants of a plantation is sufircient for it to reappear in the 

 following generation, unless it is to be supposed that the same mutation can 

 be repeated successively in different places. In Bulletin No. 12 a good 

 reproduction of this very pretty flower is found. 



Another variation is represented by the giant plants found in the Dutch 

 East Indies among the races " Deli " and " Canarie ", but apparently not 

 among the " Kedoe " race. Instead of forming a large inflorescence in 

 panicle form after 3 months' growth, the top of the plant continues to grow, 

 forming numerous small leaves in the axil of which there is sometimes, but 

 rarely, a single flower. More frequent among the giants are the forms which 

 reach great heights (16 feet and more) ; they mostly remain completely 

 sterile or in some cases, after 8 months' growth, produce a few rare flowers. 

 The writer found that these latter forms transmit their characters on a 

 constant way, while other forms which do not always exhibit all the charac- 

 ters of the giant plants produce among their descendants i, 15, 20, 21, 25, 

 31, 36, to 91 % of giant plants, according to various workers. Here the 

 Author does not admit the term mutation, as he is of opinion that this term 

 should not be ap])lied unless the hereditary factors of the initial material 

 have been examined thoroughly, which was not done with tobacco. The 

 " Deli " race, for instance, seems to him to be made up of several special 

 races transmitting their characters in a more or less constant way accor- 

 ding to external circumstances. 



