STEMS AND THEIE APPENDAGES. 51 



posing vegetable matter will yield to growing crops this 

 material in a readily soluble form. 



Soda and Potash are fonrd abundantly in all of the 

 plants belonging to the higher orders. Those growing 

 near the seashore usually contain a larger proportion of 

 soda than those growing inland, while the latter contain 

 more potash. Common potash (carbonate of potassa) is 

 a compound of carbonic acid and potassium, while soda is a 

 carbonate of sodium ; the base of both being metals hav- 

 ing a strong affinity for oxygen. All the alkalies — soda, 

 potash and ammonia, and especially in their combinations 

 mth acids — form neutral compounds from which plants 

 obtain a large portion of their mineral parts. 



Oxide of Magnesium, better known under the name of 

 Magnesia, also chlorine, iodine, bromine, alumina, man- 

 ganese, and even copper in minute quantities, exist in 

 plants, but the more important of these are found natur- 

 ally in all fertile soils, and they are seldom lacking in 

 the infertile or barren ones. 



OHAPTEE V. 



STEMS AND THEIR APPENDAGES. 



There are a vast number of simple plants that have 

 no true stems, but are composed of only single or a 

 multiplication of cells, and the growth of which con- 

 sists merely in a division or expansion of cellular tissues. 

 These plants do not possess a true vascular system, al- 

 though, in many instances, they assume an elongated 

 form, the cell uniting or expanding into a single fila- 

 ment or several parallel rows, while in others they branch 

 out in various directions, or expand into membranes, as 



