144 



FUNGOUS DISEASES OF PLANTS 



has been carefully studied, and the evidence must be accepted. 

 Subsequently, a thick wall forms about the oosphere, which now 

 properly becomes the mature egg, or oospore, 

 measuring ordinarily 25-35^ in diameter. 

 The development of an oospore may be com- 

 pleted, under favor- 

 able conditions, in 

 a single day. 



Since this fungus 

 may readily con- 

 tinue its growth 

 into dead tissues it 

 may be cultivated 

 indefinitely in Van 

 Tieghem cells or in 

 specially devised cul- 

 ture chambers, and 

 the various repro- 

 ductive processes 

 may therefore be carefully followed. It is evident that with care 

 the fungus might be isolated and grown in pure cultures. The 

 material of the genus Pythium from various hosts and localities 

 should be carefully studied and compared under control conditions, 

 as there is much doubt concerning the validity of species. 



Fig. 45. Sexual Reproduction in Pythium 

 (a, after Miyake) 



VIII. BROWN ROT OF THE LEMON 

 Pythiacystis Citrophthora R. E. Smith 



Smith, R. E. A New Fungus of Economic Importance. Bot. Gaz. 42: 215- 



221. figs. 1-3. 1906. 

 Smith, R. E. The Brown Rot of the Lemon. Calif. Agl. Exp. Sta. Built. 



190: 1-70. figs. i-2g. 1907. 



Occurrence. The brown rot of the lemon is a disease which 

 has become very prominent in the region of lemon production 

 in California during the past few years. It affects more or less 

 every operation having to do with lemon production and market- 

 ing, and at the time of the investigations which were undertaken 

 in California for its control it seemed to threaten the stability 

 of this industry. The brown rot may be found in the orchard, 



