2 VEGETABLE PHYSIOLOGY. [LESSON 1. 



5. Since the invention and constitution of Histology, as a sci- 

 ence, Physiology has made enormous strides. 



6. A knowledge of the intimate structure of the tissues, as well 

 of vegetables as of animals, has been of the greatest value to the 

 physiologist. Had the important theory of development by cells 

 not been discovered by Schawn and Schleiden in plants, the like 

 processes had remained unknown as the true principle of develop- 

 ment of the inferior animals, of the development of the Ovum in 

 the higher mammalia, and as the plan by which the human family is 

 continued. 



7. There can be no accurate knowledge of Physiology, save that 

 which is based upon an intimate acquaintance with the ultimate mi- 

 croscopical structure of all tissues; this cannot be learned from 

 books, at the present time, simply because no sufficiently illustrated 

 and voluminous work on this subject has yet been published ; under 

 the best circumstances, it appears to be most desirable to learn by the 

 actual examination of the structures themselves. 



8. It is quite true that it requires a lifetime to acquire the skill 

 to prepare such illustrations, but the devotion necessary to become 

 accomplished as a physiologist, is certainly not greater than the re- 

 quirements of Chemistry, Botany, or any other science, or greater 

 than is necessary to qualify a man for the legal or other learned pro- 

 fessions. 



9. The simple cellular plants offer illustrations of the lowest or- 

 ganized forms we are acquainted with. In them we find that a sin- 

 gle cell constitutes the entire plant. 



10. This cell is produced from its germ, assimilates nutriment, 

 converts a portion of it into the substance of its own cell-wall, se- 

 cretes a nucleus within its cavity, and ultimately produces a repro- 

 ductive germ, that is to continue the race. 



11. "When its own term of life is completed, it bursts, and liber- 

 ates the reproductive germs contained in its interior, and sets them 

 free, each being capable of going through the like series of opera- 

 tions ; or the cell wall is absorbed, thus freeing the germ. 



12. These facts are illustrated by the accompanying figures of 

 Volvox globatoT) described by Professor Ehrenberg, as an animal, 

 but which has long been known as a simple fresh water alga. A 

 perfect figure of this beautiful organism is shown at Fig. 1. 



13. The Volvoces are only to be found in stagnant pools of clear, 

 pellucid water ; placed under the field of a Microscope, they present 

 a very charming sight. In form a perfect sphere, the membrane con- 



