vii THE HISTOLOGY OF THE CELL 91 



light, (2) by leucoplasts in the underground stems, roots, &c. Starch 

 grains grow by apposition and intussusception. 



The hilum forms the organic centre of the grain. Successive layers 

 are deposited round the hilum, thus giving the grain a stratified appear- 

 ance. A ferment (diastase) can convert starch into sugar. Starch 

 grains may be simple, spuriously compound, or truly compound. 



Composition of Starch. It is built up of the same elements as 

 cellulose. It is a carbohydrate. 



Aleurone Grains. The proteids found in plants are stored up as 

 aleurone grains and proteid crystals. Each aleurone grain consists of a 

 crystalloid and a globoid. 



Formation of New Cells. New cells are produced by (i) simple cell 

 division, (2) free-cell formation. The former method takes place in 

 vegetative organs, the latter in reproductive organs. 



QUESTIONS ON CHAPTER VII 



(1) Describe the structure of a young cell, and explain how it differs 

 from a full-grown cell. 



(2) How is the cell-wall formed, and how does it grow in thickness ? 



(3) To what are the markings due which can be found in cell-walls? 



(4) Give an account of the composition and properties of cellulose. 



(5) Describe the structure of a living parenchymatous plant cell. 

 What chemical elements enter into the composition (a) of the cell-wall, 

 (b) of the protoplasm ? 



(6) How can you distinguish by the aid of the microscope a cellulose 

 wall from (a) a lignified wall, (b) a corky wall, (c) a mucilaginous wall? 



(7) What is protoplasm ? What do you know about the properties 

 of protoplasm ? 



(8) What is meant by the circulation of protoplasm? 



(9) Enumerate and give a brief account of the most important sub- 

 stances which are found in cells. 



(10) What is a chloroplast ? Where are chloroplasts found? What 

 work can they perform which makes them useful to the plant ? 



(n) Give an account of the conditions which are necessary for the 

 development of chlorophyll. 



(12) What is a leucoplast? How may a leucoplast be converted 

 into a chloroplast ? Why are leucoplasts said to be starch builders ? 



(13) What is the nature of starch? How is it formed, and what are 

 its uses ? 



(14) To what substance do the green parts of plants owe their colour ? 

 State and explain the nature of the work which green parts of plants are 

 alone able to perform. 



(15) What is an aleurone grain ? Where are aleurone grains found ? 



(16) How are new cells formed ? What kinds of cell-formations are 

 there ? 



(17) Explain clearly how starch is formed in a Potato, and from what 

 source it is derived. (1899.) 



