42 VEGETABLE HISTOLOGY. 



inward until the cell contents become separated into two equal 

 portions. This mode has been observed in some of the lower 

 algae (Spirogyra). 



&. A delicate partition of cellulose may at once be formed 

 through the middle of the cell. This is the usual mode by 

 which "tissues" are formed and growth takes place in all the 

 higher plants. 



GEMMATION. This method is found in the yeast plant and 

 its relations. (See Torula for description.) 



INTERNAL CELL FORMATION. The protoplasm of a cell breaks 

 up into two or more rounded masses, each of which eventually 

 acquires a cell-wall of its own and escapes from the parent cell 

 by the rupture or decay of the old cell-wall. Example, asco- 

 spores in lichens and some fungi and pollen grains in the 

 anthers of flowering plants. 



REJUVENESCENCE. The protoplasm aggregates into a rounded 

 mass, escapes through the cell-wall and subsequently forms a 

 new cell-wall. Commonly, before the new cell-wall forms, the 

 protoplasm forms cilia and moves about. Rejuvenescence is 

 found only among lower forms of plant life; for example, 

 (Edogonium, one of the algae. 



As was said above, Division and Rejuvenescence constitute 

 asexual reproduction. There are two modes of asexual repro- 

 duction : 



Jl. Vegetative reproduction. 

 (2. Spore reproduction. 



In the former the parent plant throws off from itself ordinary 

 vegetative cells; in the latter, specialized cells called spores 

 are formed. Examples of the first are bacteria, cell multipli- 

 cation in higher plants, multiplication in case of many plants 

 by bulbs, tubers, stolons, offsets, etc. 



Spore reproduction by the asexual process is exemplified in 

 many flowerless plants. Examples, spores on the gills of the 

 common mushroom, motile spores so commonly produced by 

 the mosses and ferns. Spores are commonly borne in a special 

 organ called a sporangium. 



UNION OF CELLS. SEXUAL REPRODUCTION. 



This consists in the coming together and blending of the pro- 

 toplasm of two distinct cells to form a new one. 



a. The uniting cells may be alike and the process is then 

 known as conjugation, and is found only in certain low forms 

 of plant life, as Mucor (a mould), Diatoms, Spirogyra, Des- 

 mids, all of which, except the first, belong to algae. 



b. The uniting cells may be unlike, the process being then 



