34 



HARDWICKE'S SCIENCE-GOSSIP. 



sequently in the second modification, while at the 

 same time the heat previously latent is evolved in 

 sufficient quantity to raise the temperature of the 

 mass 8° or 9°. 



Are we to infer from this that, besides the other 

 ways in which fats regulate the temperature of the 

 organisms in which they occur, nature, by endowing 

 them with the capacity of pleomorphism, has in- 

 vested them with an additional and special power of 

 compensating sudden vicissitudes of temperature ? 



I shall not trouble you with mora than one other 

 illustration of pleomorphism as "manifested by non- 

 living matter. In a late number of the " Proceed- 

 ings of the Royal Society," it is shown, in a paper 

 by Mr. Eodwell, that the iodide of silver exists in 

 three allotropic forms": viz., (a) at temperatures 

 between 241° and its fusing-point, which is about 

 842°, as a plastic, tenacious, amorphous substance, 

 possessing a reddish colour, and transparent to 

 ligbt ; (f3) at temperatures below 241°, as a brittle, 

 opaque, greenish-grey crystalline mass ; and (y), if 

 fused and poured into cold water, as an amorphous, 

 very brittle, yellow, opaque substance. 



But the most remarkable and auomalous character 

 of this body is, that, in cooling after being melted, 

 the following effects may be observed :— (a) At the 

 moment of solidification a very considerable con- 

 traction takes place ; (/3) the solid, on further cool- 

 ing, undergoes slight and regular contraction, after 

 the manner of solid bodies in general, until (y) 

 at or about 241° it undergoes sudden and violent 

 expansion, passing from the amorphous into the 

 crystalline condition ; (o) after undergoing this ex- 

 pansion, the mass, on further cooling, undergoes 

 slight expansion, and (t) the co-efficient of con- 

 traction diminishes as the temperature decreases 

 (or, otherwise expressed, the co-efficient of contrac- 

 tion augments with the temperature) . 



Hitherto I have spoken of dead matter only, and 

 of the changes of which it is susceptible without 

 losing its identity. But in the world of life we 

 meet with phenomena which, although I confess, it 

 is on any view of their nature difficult to compare 

 them with those I have been speaking of, yet sug- 

 gest so many analogies with the latter, that I cannot 

 help speaking of some few of them in this con- 

 nection. 



The case of the metamorphoses of insects is one 

 so familiar to most persons, that I need do no more 

 than refer to it. 



My next illustration is from a homely source. 

 We are all familiar with an unwelcome guest,'which, 

 in the form of a white down, takes up his quarters 

 upon the surface of jams and preserved fruits that 

 have begun to decompose. This white down con- 

 sists of a fungus known as the Aspergillus glaucus, 

 which, after its spores have ripened, assumes a grey 

 or dull-green colour. The vegetative portions of 

 this fungus— that is to say, all that part of it which 



\ is not immediately concerned with the production 

 of the fruit, — the mycelium, as it is called— con- 

 sists of a series of interlacing and branching cylin- 

 drical threads made up of elongated cells placed 

 end to end, and generally filled, at least in the 

 young state, with a liquid in which very fine gra- 

 nules appear to be suspended, and to which the 

 name protoplasm is given. These threads keep 

 constantly elongating by additions to their points, 

 and give off branches in all directions, which again 

 elongate in a similar way. Some of these threads 

 overspread the surface, others ramify in every di- 

 rection through the substance of the matter upon 

 which they grow. From the superficial threads 

 certain branches rise perpendicularly into the air to 

 the length of about s'^th of an inch, and these 

 branches bear at their summits little globular heads. 

 From the upper half of each of these heads issues a 

 series of small, closely-packed processes, at the free 

 extremity of each of which a small round protube- 

 rance is formed, which eventually becomes a spore. 

 No sooner is one spore formed than the formation 

 of a second commences on the same spot, pushing 

 forward the one first formed, and to this succeeds 

 another, and then still another, until some ten or 

 more have been produced on each of the processes— 

 sterigmata, as they are called, — the whole series 

 remaining connected for a time, and forming a 

 chain of spores extending in the direction of the 

 axis of the sterigma. These spores, each of which 

 is about urolith of an inch in diameter, are distin- 

 guished by the name conidia : it is they which, 

 when in mass, constitute the fine dust of a grey- 

 green colour already mentioned. 



I have been thus minute in describing the pecu- 

 liarities of the conidiiferous form of fructification 

 of Aspergillus glaucus, because they are more or less 

 typical of what we meet with in the case of many 

 other fungi. 



But what I wish to direct attention to more par- 

 ticularly is, that the same mycelium which produces 

 this kind of fruit, these conidia, also gives rise to 

 another set of reproductive organs. When the 

 production of conidia is drawing to a close, a 

 number^of small fine branches issue from the my- 

 celium. After attaining a short length, each of 

 these assumes the form of four or six turns of a 

 corkscrew. Eventually, these turns approach each 

 other till they form a hollow screw ; a small branch 

 now issues from the base of the spiral, and extends 

 till its free extremity meets that of the spiral, with 

 which it then unites. This union is held to be the 

 equivalent of impregnation among the higher plants. 

 Other branches then issue in all directions, inter- 

 lacing with one another, till they form a close hull 

 over the spiral ; the whole presenting the appear- 

 ance of a little yellow spherule. Each of these 

 yellow spherules when mature contains a number 

 of bags, each bag (ase/cs) containing eight spores, 



