28 



VENTILATION AND COVERING OF HOT-HOUSES. 



its total absence, requiring- keen sight or a lens to discover it, a 

 variation impossible in the course of generations since the crea- 

 tion of vegetables before the sun shone upon the earth ? Is it a 

 feature of difference as conspicuous as those which daily occur 

 amongst seminal varieties ? And does it not derive its import- 

 ance (for I do not underrate its importance) merely from its 

 having become in all its further development a fixed character 

 and the badge of a peculiar family? It must be remembered, 

 that even amongst the Pancratiform plants, Urceolina has even 

 less rudiment of a cup than N. deficiens, and that ill Pentlandia, 

 which in every other respect is a perfect Stenomesson, with 

 which it is perhaps capable of breeding, there is no vestige of 

 the membrane which forms a cup. Then turn to Alstroemeria, 

 and look at Alstroemeria pygmaea, Herb. Am., pi. 8, and see 

 something like the first attempt to produce that race, a solitary 

 pale-yellow flower on a short stalk, with a few narrow leaves at 

 its base, and see how near it comes to the Tapeinaegle humilis ; 

 having, however, a palmated tuber, and therewith the disposition 

 to a leaf-bearing stalk — a variation occurring in some genera 

 amongst plants of which the flowers are conformable, as in the 

 group of Sisyrhynchium. The round turnip has this very year 

 degenerated into a bunch of keys in my fields, in consequence of 

 the state of the atmosphere, as I know to my cost ; and since the 

 change of weather some turnips are beginning to form a round 

 root on the top of the bunch. Here I see, to my cost, how the 

 condition of earth, air, and water can affect the conformation of 

 a root ; and I learn what the changes that have taken place 

 since the great era of the creation of vegetables may have done 

 in that respect. I should take Zephyranthes minima, and 

 Gracilis, Carpolyza, Hessea, and Acis, to be nearest to the 

 created type of Amaryllidaceae. 



II. — On the Ventilation and Covering of Hot-houses. By Mr. 

 Thomas Moore. 



(Communicated Sept. 19, 1846.) 



It is a well-known fact, that in producing an artificial climate 

 for the growth of tropical plants, or for the purpose of forcing 

 those which are natives of more temperate regions, the less 

 amount of artificial heat which is applied in keeping up a proper 

 degree of temperature (so that this is done), the better will that 

 climate be suited to its intended purpose, all other things being 

 equal ; and it is especially at night when the plants are surrounded 

 by darkness, and when excitement would be more than ever hurt- 

 ful, that this becomes of increased importance. At night, too, 



