26 THE VEGETABLE CELL ]N GENERAL. 



know them to be organs and even organisms. Histology therC' 

 fore begins with the coll in its independent condition. 



117. A complete and living vegetable cell consists of a cell- 

 wall enclosing certain essential contents. 



118. In their earliest state some of the lower plants exist as 

 a mass of motile living matter, not bounded by anj- envelope. 

 But in all plants of the higher grades the living matter of the 

 cell is from the verj- first protected by a cell- wall. 



119. That which is essential to the vital activity of a cell is an 

 apparently half-solid sul)Stance, — -protoplasm. With the prop- 

 erties of protoplasm as a living thing. Physiology and not His- 

 tology" is immediatel3' concerned. But it is necessary throughout 

 the stud}' of Histology to make a distinction between the cells 

 which are vitally acti\e and those which serve chiefly or wholly- 

 some mechanical end ; and hence attention mnst be called at the 

 outset to the means b}' which the lixing matter of the cell can be 

 identified. 



120. Protoplasm exists in all j'oung cells — for instance, in 

 the soft cone of tissue in buds, in root-tips, and other i)oints of 

 growth — as a nearly transparent or finely granular substance.' 

 It completely fills the interior of very young cells, but with 

 increase of the cells in size there arise cavities (vacuoles) con- 

 tainuig sap, and these bj' their enlargement and confluence may 

 appear to occup}' the entire space within the cell. If, however, 

 such a cell be acted upon by anything which causes contraction 



(2) Make a tlnii section through the petiole of a begonia or some common 

 house-plant, and observe the granules iinbedded in the protoplasm (clilorophyll- 

 gramdes); notice also crystals, either in masses or single. 



(3) Examine a thin section through dry pine wood, test with iodine, and 

 observe the absence of protoplasmic matters. Examiuc in the same way any 

 hard wood. 



(4) Make a section through any starchy seed, for instance a common bean, 

 and treat it with a solution of iodine ; notice the distribution of protoplasmic 

 matters in the form of thin irregular films throughout the cells. Examine a 

 similar section in oil, and see what differences, if any, can be detected. Prob- 

 ably the jiresence of protein granules will be made! out. 



From these jireliminary examinations a beginner will have demonstrated 

 the protoplasmic matter in its active, resting, and reserve states ; he will have 

 seen chlorophyll, the nucleus, and starch, the chief form in wliich food is 

 stored in plants. He will also have seen a few of the more common crystals. 



After such a study the student is urged to examine practically the charac- 

 teristics of the cell-wall and the cell-contents as they are presented in this 

 chapter-. 



1 By the use of staining agents, especially haamatoxylin, protoplasm can in 

 many cases be shown to possess a complicated mesh of very delicate fibre.'-. 



