MONTHLY CALENDAR. 635 



given at once, and caution used to prevent the artificial and solar heat exert- 

 ing their full force simultaneously. Few plants are proof against the disas- 

 trous shi-ivelliug influences of being thus placed between two fires : neither is 

 . it at all necessary to give air daily. Often for a week together, a sweet genial 

 atmosphere may be maintained within, when the outside air is totally unfit for 

 admission. Nothing requires greater practical knowledge and sounder judg- 

 ment than the ventilation of tropical plant-structures in winter; a happy 

 medium between the close glass-case and cutting-hurricane system is the 

 grand desideratum, and nothing but enlightened experience, and an innate 

 sympathy with the plants cultivated, can confer the necessary qualifications 

 for the performance of this important operation. It should ever be borne 

 in mind, that plants are endowed with the power of purifying their own 

 atmosphere within certain limits ; and that, consequentl}', the incessant 

 admission of ungenial, harsh, external air, is not essential to their healthy 

 existence. On the other hand, they rapidly exhaust the supply of car- 

 bonic acid gas present in a given quantity of air, and, therefore, an occa- 

 sional change of air is essential to furnish them with food. Not only that, — 

 the quantity of oxygen liberated bears a relative proportion to the amount 

 of carbonic acid gas consumed ; consequently, the less of the latter appro- 

 priated by plants, the less of the former is given back to the air, and it 

 becomes the sooner deteriorated in consequence. It therefore follows, 

 that while for a limited period plants may thrive in the same atmosphere, 

 their constitution and necessary wants demand a change sooner or later. 

 The fi-equency of the change i-equired will very much depend upon the 

 energy with which the vital force is being expended. In other words, 

 the faster the plant grows, the more fresh air will be necessary. 

 Now, as winter is the dormant period, less external air is requisite in 

 winter than at any other period of the year. The fact thus elucidated is of 

 immense practical importance to the cultivator ; for just when it is well-nigh 

 impossible to admit such air, we discover, both by science and experience, 

 that its presence may be largely dispensed with. This remark is equally ap- 

 plicable to the cultivation of orchids ; it even applies with double force to 

 them ; for, as most of these will now be comparatively dormant, this house 

 may often remain for a month without fresh air with impunity. The great 

 points are a dry atmosphere and a comparatively low temjDerature, — from 65° 

 to 70°, and the maintenance of all in a dormant state. Now is the great 

 cleaning season ; every scale, bug, earwig, cricket, &c., must now be ferreted 

 out and destroyed. 



1978. Forcing-Fit. — Introduce the first batch of rhododendrons, kalmias, 

 Ghent and Indian azaleas, &c. ; also some tea and hybrid perpetual roses, and 

 early-flowering and sweet-scented geraniums, white and Anne Boleyn pinks, 

 perpetual carnations, and lily of the valley ; also Salvia gesneraflora, late 

 gesneras, and Euphorbia polygonifolia. Towards the end of the month, some 

 hyacinths, tulips, &c., potted towards the end of September, should now bo 

 pushed forward in this structure. Procure, and pot forthwith, the whole^ 



