56 MASSACHUSETTS HORTICULTURAL SOCIETY. 



eflfects of these different factors and, therefore, no attempt will be 

 made to arrive at ultimate causes. 



The Water Relation. 



The ^^•ater relation is invariably a most important one, and a 

 few typical instances of how it operates may be cited. The com- 

 mon disease of the cabbage in many sections of the country is the 

 black rot, or black heart, a bacterial disease. In order that the 

 minute organisms causing this disease may gain entrance to the 

 leaf, the presence of beads of water around the margin of the leaf 

 is demanded. Such beads of water in this position are a normal 

 occurrence on cool mornings after a warm day. The roots of the 

 plant are active in the warm soil, while the loss of water from the 

 plant by evaporation is checked, so that these droplets are filtered 

 out through certain water pores of the leaves. In this case we can 

 scarcely say that there is lessened vigor on the part of the cabbage. 

 The essential point is that there is a water connection between the 

 external and internal environment. If we consider remedies it is 

 evident that the check which is to be applied to the spread of this 

 disease, especially in the seed bed, is one which would prevent the 

 formation, as far as possible, of such droplets, and this can perhaps 

 best be done by a regulation of the conditions through screens or 

 shading. Unfortunately, some root infections also occur. 



Mr. Stone in this State, and iNIr. Smith in California, seem to have 

 clearly demonstrated that there exists between the asparagus rust 

 and its host a very definite water relation. During the dry summer 

 of 1905, this fungus in INIassachusetts was confined to the coarsest 

 soils easily affected by drought, and each of the severe outbreaks 

 since 1896 has been identified with a similar condition, or at least 

 with long periods of relatively dry weather between rainfalls. At 

 such time the addition of water, as through irrigation, is desirable. 

 Efficient cultivation affording perhaps a better soil mulch is also 

 recommended. On the other hand, it is to be inferred from the 

 work of others that too much water in the sub-stratum, or over- 

 irrigation, is alone sufficient to intensify what is in other fields a 

 very mild epidemic. In substance, the relation between the aspar- 



