308 



THE GARDENER'S MONTHLY 



[ October. 



To this it may be answered that wood in it? 

 natural conchtion cannot be ignited by the tem- 

 ficrature over attained by any of the steam-heat- 

 ing apparatus in use. In this city tlie steam- 

 pipes are often in direct contact with tlie wood ; 

 and this is the case with tlie building in which 

 our journal is published, and even in the room in 

 which we write, but we apprehend no danger as 

 long as no other cause of heat development 

 comes to the aid of the heat produced by the 

 steam. Such causes are animal or vegetable oils 

 and fats, especially drying oils and varnishes. 

 Almost everybody knows the effect when saw- 

 dust or rags are saturated with such oil — sponta- 

 neous combustion may be the result, by reason 

 of the access of air to the interior of the highly 

 porous mass which constitutes a heap of sawdust 

 or rags. Oil on a wooden board will not produce 

 spontaneous combustion, as from want of poro- 

 sity the air has not sufficient access to the inte- 

 i-ior to produce enough simultaneous oxidation 

 to raise the temperature to the point of ignition ; 

 but if steam-heat comes to the aid of the oil- 

 soaked wood, it may supply the function of the 

 oxidizing air penetrating the interior, and raise 

 the temperature to the point of ignition, and we 

 are perfectly satisfied that if the rare cases of ig- 

 nition of wood by steam-heat were investigated, 

 it would be found that a secondary cause was 

 added to the heat produced by the steam, or by 

 its condensation in the pipes ; such secondary 

 causes being wasted oil or the throwing away of 

 a burning match, which would not set fire to 

 cold wood, but might do so to wood thoroughly 

 heated and dried. Even matches laying about 

 and carelessly treated may ignite by steam-heat 

 and set fire to papers, or the wood itself. But if 

 such secondary causes are only guarded against, 

 steam-heat maybe considered as the safest mode 

 of heating buildings — uniformly safer than cur- 

 rents of hot air, which may carry sparks along 

 and fan an incipient fire rapidly into a blaze. In 

 fact, the causes of fire from steam-heat are com- 

 paratively rare, while those from hot-air furnaces 

 are very common. — Manufacturer and Builder. 



Abies Fraseri. — At a recent meeting of the 

 Academy of Natural Sciences of Philadelphia, 

 Dr. Engelmann, of St. Louis, spoke about Abies 

 Fraseri, the very local species of the highest 

 mountains of North Carolina, which he had just 

 visited, together with several botanical friends, 

 members of this Society. This is the tree which 

 caused these mountains to be designated the 



Black Mountains, giving their summits thaf 

 sombre hue for which they are known ; they 

 seem to grow nowhere but on these mountains, 

 and only on those that reach up to or above 

 (),0()0 feet altitude. The northern localities 

 claimed for the species rest on confusion with 

 forms of Abies balsamea, the common northern 

 Balsam, of which our tree may be claimed to be 

 the southern representative. A. balsamea does 

 not seem to extend southward further than the 

 Virginian mountain region, and it would be in- 

 teresting to ascertain how near both species ap- 

 proach each other. Besides the well-known 

 characters of the cones and their cusps, excel- 

 lent distinctions are found in the structure of the 

 leaves of both species. It may not be generally 

 known, though it is a fact to which, since seve- 

 ral 3'ears, some European botanists have called 

 attention, that the anatomical structure of the 

 leaves of these species, as well as of Conifers in 

 general, is extremely various, and that this struc- 

 ture well characterizes many species, and is one 

 of the safest means to arrange them in natural 

 groups. Abies Fraseri and balsamea are so 

 nearly allied, that without fruit they are con- 

 stantly confounded, but the structure of the 

 leaves will always distinguish them so well that 

 a single leaf, or even a fragment of one, will in- 

 variably solve all difliculty. The leaves of Abies 

 have under the epidermis, and between it and 

 the cells of the parenchyma, which are full of 

 chlorophyll, an arrangement of cells of thick 

 walls, elongate form, and destitute of chlorophyll, 

 analagous to bast cells, Avhich have been called 

 hypodermic cells ; we find them in all species of 

 Abies on the edges and on the keel, where they 

 strengthen the leaf, but their distribution under 

 the epidermis of the upper side of the leaf is very 

 different in different species — they may be want- 

 ing there altogether, or may be differently 

 grouped, or may extend over the whole upper 

 surface; now in all forms of A. balsamea they 

 are there almost entirely absent, even in those 

 of the highest New England mountains, while 

 A. Fraseri exhibits under the microscope a con- 

 tinuous hypodermic stratum of them. 



Insects and Fertilization. — Pretty flowers are 

 thought to have been so made in order to attract 

 insects, and thus gain an advantage in cross-fer- 

 tilization. There is no good without its evil, and 

 thus we have pretty maidens to pull the pretty 

 flowers, and ardent botanists to pull out and dry 

 them before the insect-fertilized flower has a 



