TITE VEGETABLE CELL. 51 



Throughout all these changes the cell-wall may retain its 

 original thinness and transparency, but very frequently it 

 becomes thickened and opaque by the successive deposition of - 

 layers of solid matter, while at the same time its fluid con- 

 tents disappear and its individual growth is at an end. The 

 thickening is generally not uniform over its whole surface, 

 but presents frequent interruptions, so that the cell appears 

 punctured with numerous round pores, or creviced, or covered 

 with a network, or with a spirally wound-up band, or with 

 a succession of opaque rings ; and from all these modifica- 

 tions of solidification and growth result the endless varieties of 

 texture which we admire in the vegetable kingdom, and which 

 must appear the more astonishing when we consider the simple 

 elementary form from which they all derive their origin. 



In most cases the growing cells multiply by duplicate subdi- 

 vision, each half increasing in length, and again dividing through 

 a transverse partition, or else new cells form in the interior of a 

 parent cell and expanding burst open the shell or case in which 

 they were contained. Thus the growth of all plants proceeds 

 by a constant multiplication of cells whose number frequently 

 increases to an incredible extent as a cubic inch of soft cellular 

 parenchyma contains more than 100,000,000 individual cells. 

 The simplest plants, the confervas, algse, lichens and mush- 

 rooms, consist only of soft cellular tissues, and in these, owing 

 to their loose nature, growth frequently proceeds with a most 

 marvellous celerity. In twenty-five minutes a mushroom 

 the Phallus foetidus shoots up three inches high, and in ano- 

 ther species the Bovista gigantea 20,000 new cells form every 

 minute, so that in a single night it swells from the size of a 

 pin's head to that of a large pumpkin. Thus also the Nereo- 

 cystis lutkeana, an alga occurring on the north-west coast of 

 America, which has stems resembling whipcord, three hundred 

 feet in length and terminating with a bunch of leaves each 

 thirty or forty feet long, is but the produce of a single summer, 

 so that it is hardly an exaggeration to say that one might see it 

 grow. A proper seed formation does not take place in these in- 

 ferior plants, they generally multiply by the emission of spores 

 simple cells which are often generated in truly incalculable 

 numbers. More than 1 0,000,000 of spores have been found in a 

 single specimen of Eeticularia maxima, a mushroom growing on 



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