214 GENERAL BOTANY 



and reproductive organs, while the anatomy of a cat would include 

 the gross structure of the tissues and the main organs of the body. 



Histology. In plants histology is easily confused with anatomy, 

 since each includes the microscopic structure of the tissues and 

 organs, although histology in plants comprehends more detailed 

 microscopic structures of the cell units which make up the tis- 

 sues and organs than is the case in plant anatomy. In animals, 

 however, histology is distinct from anatomy as it is generally 

 understood, since histology in animals means the microscopic 

 structure of the cell units of the parts of the animal body, which 

 are observed in gross in anatomical studies. 



Cytology. Cytology is the newest of the branches of biology 

 yet mentioned, and includes the minute microscopic structure 

 of the cell units of living organisms and also of the ultimate 

 structure of living matter. 



Embryology. As the term is commonly understood, embryology 

 applies to the processes of development of an organism from the 

 early divisions of the fertilized egg to the adult stage, in which the 

 various organs and tissues have reached their ultimate form and 

 structure. Embryology, like morphology, may include simply the 

 processes and stages in the development of an individual organism, 

 or it may be comparative in its nature and include a comparison 

 of the developmental processes of a series of related organisms. 



Physiology. Opposed to morphology and its subdivisions is 

 physiology, which deals with the functions of organs and parts 

 of single individuals or with the activities of organisms in gen- 

 eral. The field of physiology is rapidly extending to-day into 

 the older fields of biology, as is indicated by the newer studies 

 in experimental morphology, ecology, embryology, and evolu- 

 tion. In all of these new fields of study the facts accepted by 

 older systematic and morphological biology are being tested by 

 physiological experiments and observations. 



Ecology. The newest of the main subdivisions of biological 

 science is ecology, which comprehends the relation of plants 

 and animals to their environment and the relation which exists 

 between form, structure, and environmental influence. Applied 

 to plants it includes the effects of light, heat, moisture, and soil 



