The science of life : fully illustrated in tone and line and including many diagrams

BOOK 2

containing spores, they may have tangled fibres in them, which uncoil like springs when they are moistened, thus jerking out the spores, which are then distributed by wind.

The process by which the inchoate,

Fd

Ig. 119. From the spore (seen highly magnified at 1) an Ameba-like creature emerges ; it temporarily acquires a long, whip-like tail, so that it can swim or creep as it pleases. Presently these creatures collect and flow together into protoplasmic

The growth of a Slime-mould.

Sheets. This union is drawn to a smaller scale below.

creeping film of protoplasm converts itself into a number of highly specialized and

elaborated sporangia is extraordinarily interesting. It is almost as if a lump of plasticine were suddenly to pull itself

together and model itself into a working clock. In those species which have stalked sporangia, for example, the protoplasmic sheet slowly heaps together in a number of places,

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THE SGIENCE OF LIFE

CHAPTER 6

acquiring a warty surface ; the warts grow slowly upwards and a solid stalk is formed at their core by a hardening of their own substance ; the viscid, living fluid climbs up this stalk as it makes it and, at the top, it hardens and elaborates itself into the complicated structure that we have briefly described. In this manner the whole plasmodium turns itself into a tiny forest of sporangia—the process taking somewhere about a day.

The ripe spores, a few thousandths

of a millimetre across, are blown about by the wind, and if they settle in a damp place with a supply of decaying organic matter for food they hatch and develop. The creature that escapes from the hard spore-shell is of microscopic dimensions ; it is like a combination of an amoeba and a flagellate, having a plastic body and a long whip-like tail. It can either creep like an amoeba or dance like a flagellate. Moreover, it reproduces by division as the protozoa do, and so may give rise to a great number of similar “‘swarm-cells.”? After a time these swarm-cells show a sociable tendency ; they collect together in groups and they fuse with each other in pairs, completely and unreservedly, like the spermatozoon with the ovum. The result of this simple sexual process is a microscopic plasmodium, a miniature of the protoplasmic sheet with which we began our description. This tiny film creeps about, feeding on bacteria and the like and slowly growing, but it does not develop directly into the fully-grown plasmodium—at least, not by its own unaided efforts. It takes more than one to make an adult. Whenever the tiny creature meets another such sheet belonging to the same species, it mixes eagerly with the new acquaintance, the two forming a single living mass. And so on. So that the final large plasmodium is in reality a union of hundreds of dancing swarm-spores that have completely merged their individuality into one shapeless gelatinous sheet. Imagine that whenever two people meet each other in the street they run together into one blob, as drops of water run together, so that ultimately the whole population of a town is rolled up into a gigantic mass of livmg substance that creeps about like a single creature; that is the sort of thing that happens as a matter of course in the lifehistory of a slime-fungus.