ROOT CROPS 



293 



thinned when three or four leaves have developed to one in 

 a place. No material difference in yield appears to result from 

 these two methods, so that the method employed will depend on 

 the convenience and expense. The distance 

 apart in the row will depend on the purpose 

 for which the cabbages are grown. Where 

 they are sold for ordinary culinary pur- 

 poses a larger number of small cabbages 

 are desired, while for forage purposes or 

 for sauerkraut a smaller number of large 

 cabbages is best. Early seeding is essential 

 to high yields, earlier even than for man- 

 gel-wurzels, although common turnips may 

 be sown as a catch crop as late as July. 



370. Enemies. All plants of the mustard 

 family are subject to the attacks of the 

 club-root or finger-and-toe disease (Plas- 

 modiophora brassicae Wor.) which causes 

 the root to take on abnormal shapes and 

 may seriously reduce the yield; and by Carter - s Purple _ top Mam . 

 black rot (Pseudomonas campestris (Pam- moth turnip, showing 



ix T, r "-.!_ \ *.! t- ^ i the variation in size of 



mel) Erw. Smith). Both are best combated early sown above and 

 by a rotation of crops. Lining is also con- late sown below. 

 sidered beneficial. 



Black rot is a bacterial disease. The disease usually makes its appearance 

 on the outer leaves of the cabbage, near the margin, entering by way of the 

 large marginal water pores, but infection may also occur through the roots 

 or at the base of the leaf close to the stem. The disease spreads through the 

 entire plant by means of the veins. The leaves, being deprived of water, 

 become dry, turn yellow, and perish. A diseased leaf shows the blackened 

 veins, or a cross-section of a diseased leaf or stem discloses black spots instead 

 of the faint yellowish spots of a healthy plant. So far as known, the disease 

 spreads by contact, or by inoculation of the leaves by leaf-eating insects, or 

 of the soil with germs which are believed to pass the winter in the soil, or 

 which may be incorporated in manure from stock fed on diseased plants. It 

 is also believed to be propagated by means of inoculated cabbage seed whicn 

 may occur on the market. In this case the precaution is recommended to 



