1885. 



AND HORTICULTURIST. 



107 



as well. Just how much salt to employ must be 

 a matter of careful experiment. Lime water de- 

 stroys some of these terrestrial creatures without 

 Injuring the plants, and it may be of service as 

 against this enemy. — Ed. G. M.] 



Cause of Mildew on Roses and Other 

 Plants. — " Rose Grower " says : "I note in the 

 Gardeners' Monthly remedies for the cure of 

 mildew. Is anything known of its cause and pre- 

 vention ?" 



[Under the name of mildew we are speaking of 

 small funguses. These, like the whole mushroom 

 family, only grow when there are combined 

 moisture and a degree of heat just suited to them. 

 They seem to require exact conditions for growth 

 to a fine point not required by a higher order of 

 vegetation. We may for instance expose a piece 

 of bread to the weather. If it get wet and the 

 temperature is but a few degrees above freezing 

 point, no fungus at once appears. If the tempera- 

 ture be above 50°, no fungus appears; at least not 

 the cob-webby form which is so destructive to 

 vegetation. But if the temperature be about the dew 

 point, the bread will be found as soon as the dew 

 is off completely covered with a fine silky organ- 

 ism. It was the exact temperature in connection 

 with the moisture that induced the rapid fungous 

 growth. Now in rose culture few are troubled by 

 mildew; when a temperature of 55° is steadily 

 maintained in connection with the humidity of 

 the atmosphere. If a draft of cool air be admitted 

 so as to suddenly alter the hygrometric conditions, 

 or the temperature in connection therewith, mil- 

 dew may follow. Sulphur applications may kill 

 it after it has started. 



But the conditions of the plant may favor the 

 growth. There is no doubt now but mildews will 

 attack perfectly healthy vegetation, but it is also 

 true that they prefer that which is either dead or 

 with low vital power to that which is strong and 

 vigorous. The weakest leaves are the first at- 

 tacked. It is therefore wise in the rose grower to 

 study those laws of health related to roses or other 

 plants. A large number of rose growers have 

 plants that by bad treatment are under low vital 

 conditions, and these are unquestionably more 

 liable to mildew than perfectly healthy plants. 

 The average rose grower knows very little about 

 the laws of health as applied to the plants he 

 grows. — Ed. G. M.] 



Greenhouse Flues. — " D. B. C," Dubois, Pa., 

 writes: " 1 have built a new greenhouse which I 

 want to heat by flue. Would you be kind enough 



to inform me what sized grate to use, and also 

 the size of drain pipe for a house 20x50 ? Is there 

 any way to clean those flues besides brushing 

 them out ? Is there any chemical process for 

 cleaning them ? The flue I have in use now is 

 only to heat a small house, and I find it very diffi- 

 cult to keep clean." 



[Eighteen or twenty inch bars ought to be 

 enough for a grate for such a house. Ordinary 

 drain pipe is vitrified or glazed. We have not 

 found these as good as the unglazed ones, and we 

 find those made of fire clay superior. For your 

 house one with a six-inch bore would do but for 

 the soot from bituminous coal choking it so soon. 

 Eight inches would be better. 



There is no chemical that we know of to clean 

 these flues. In our case we had a moveable col- 

 lar made for a number of sections. In this way a 

 section here and there can be wholly taken out, 

 and the rest easily cleaned. These collars must 

 have a piece of wire fastened around them, or 

 they will break when being filled with mortar, 

 clay, or whatever may be used to close the joints. 

 Wire should also be put around each piece of pipe 

 to guard against the escape of gas should any one 

 crack. The writer has had such pipes in a house 

 for twenty years without renewing a single section, 

 and working entirely to satisfaction. — Ed. G. M.] 



Double O.xalis D. R. Woods, New Brighton, 



Pa., writes : — " In reply to your correspondent on 

 p. 43, February number Gardeners' Monthly, 

 would say Oxalis lutea plena is a desirable bulb. 

 Its flowers are very double, but do not exceed 

 three-quarters of an inch in diameter. In regard 

 to lutea plena being the correct name we do not 

 know. The one to which we refer we firet saw 

 noted in the list of a Pennsylvania florist, and be- 

 lieving it was new we sent an order for all he had 

 of it. We have grown hundreds of it during the 

 past two years and are highly pleased with it, both 

 as a basket and pot plant. By referring to ' Rand's 

 Book of Bulbs,' pubhshed in 1866, we find a double 

 yellow Oxalis mentioned therein. This may or 

 may not be the same. The Editor is correct in 

 saying ' it would look like a very small dandelion,' 

 nevertheless when in full bloom it is very pretty." 



NEW OR RARE PLANTS-. 



New Varieties of Ferns. — It makes little 

 difference to a lover of plants whether the little 

 beauty he admires is what a botanist calls a species, 

 or only a variety. If they are distinct and lovely 

 it is all the same. The two we now illustrate are 



