222 HOW PLANTS GROW. 



We cannot now particularise the numerous tissues. That 

 would mean a minute study of the anatomy of root, stem, and 

 leaf, It is enough to say that the whole plant is made up of cell- 

 fusions and tissues in varying proportion, both these being com- 

 posed of cells, in one case fused, in the other not so. In both 

 cases, cells, and cells only, form the groups ; the two groups make 

 up the plant. We thus find our starting axiom to be true. 



We must next ascertain how from any one cell, other cells are 

 formed. We have seen how they are fused to produce vessels, 

 but how are they able to produce the tissues spoken of — groups of 

 similar and distinguishable elements ? In other words. What is 

 Cell-formation ? Here again we must be content with a few broad 

 facts, and let theories alone. 



(c) Cell-Formation and Growth. 



By this is meant the origin and multiplication of cells, two 

 processes which are identical, if we shut out spontaneous genera- 

 tion, and the '' fortuitous concourse of atoms," and base our study 

 on the axiom, not as yet invaUdated, " Omnis cellula e cellula." 



There are three types of Cell-formation : — 



I. — Refiewal^ or Rejuvenescence. This is the forming of a new 

 cell from the entire contents of an already existing one. It is 

 seen among the Algce^ where a " swarm-spore" is formed out of the 

 entire protoplasm of a vegetative cell, swims for a time by means 

 of its ciha, secretes a cellulose coat, and finally settles down, to 

 presently form in its turn a new swarm-spore. 



2. — Conjugation. Two cells approach each other, an aperture 

 is formed at their junction, complete union of the two masses of 

 protoplasm ensues, and " spores " are produced which in turn 

 become independent organisms. This is seen in many Algce and 

 Fungi: — in Spirogyra^ for example, and the Conjugatce 2iS an order, 

 and in Mucor^ the ordinary green mould. 



3. — Cell-Multiplicatio?i. This is the formation of two or more 

 protoplasm masses out of one original mass ; each of the three 

 modes named begins by the protoplasm losing its motile power, and 

 shrinking into a somewhat spherical form. If the " mother-cell " 

 contains a nucleus, this contraction is preceded by the formation of 

 fresh nuclei, destined for the "daughter-cells," or new ones. This 

 formation may come about either by simple division of the original 



