250 THE GARDENER. [June 



the back motion), " any further than that the upper strata travel faster than 

 the colder under strata." Now if the colder under stratum did travel uphill, 

 there is no doubt it would do so at a slower pace than the upper and hotter 

 stratum. But when each stratum reaches the highest point and commences the 

 downhill journey in the return-pipes, how do they behave as regards their 

 respective rates of travelling? Does the upper and hotter stratum travel faster 

 than the under and colder stratum on the descending course ? and if not, may I ask 

 Mr Makeuzie to explain why not ? According to my ideas of circulation, the 

 colder volumes of water should lead in the race from the highest to the lowest 

 point, whereas, according to this strata theory of circulation, the hotter 

 volumes make the circuit of the pipes in less time than the colder. In an 

 apparatus where this takes place the circulation is bad : the heat in the stoke- 

 hole, where it is not wanted, is excessive ; and in the houses, where it would be of 

 use, it is unsteady and unsatisfactory. In conclusion, I quite agree with Mr 

 Makenzie when he says it is evident that I have not mastered the subject. It 

 is difficult to master any subject, however simple, and heating by hot water is 

 rather a complicated one. The readers of 'The Gardener,' however, will form 

 their own opinions as to whether Mr Makenzie's or my ideas on the question 

 are the more correct. J. Hammond. 



Brayton Hall, \2th May 1879. 



[We beg to thank several correspondents for their contributions on this sub- 

 ject, and regret that we cannot make room for them this month. — Ed.] 



THE CULTIVATION OF CLEMATIS. 

 "Without doubt the varieties of Clematis have risen of late years to a 

 very high degree of excellence, and we know of no other plants that 

 can be used for such a variety of purposes, and none is more worthy 

 of extended cultivation in private places. Yet we do not see them 

 grown so extensively as they deserve to be, especially in pots, for 

 the decoration of plant-houses. They are alike suitable for the or- 

 namentation of rooms, either in small pots or in large ones ; and 

 the plants may be trained round balloon trellises, or umbrella-shaped 

 standards, or in any conceivable form to suit the purpose and taste 

 of the cultivator. 



They are at home as climbers in the greenhouse or conservatory ; 

 and what can produce a more pleasing effect than these lovely plants 

 when in flower, with their various and delicate shades of colour, hang- 

 ing in festoons from the roof of plant-houses, intermixed with ever- 

 green plants such as Passifloras, Tacsonias, &c, which considerably 

 assist to hide the bareness of the Clematis when in a leafless state 1 

 We are aware the Clematis is somewhat objected to because it is de- 

 ciduous j nevertheless, with a selection of sorts, some can be had in 

 bloom nearly, if not quite, all the year. And this objection can be 

 overcome by growing the plants in large pots, and removing them 



