PLASTIDS. 9 



after which the effect upon fresh material of potassic hydrate, 

 both the concentrated and the dilute solutions, should be care- 

 fully watched. In these examinations it will be well to practise 

 with the reagents without lifting the cover-glass (see 17 and 20). 



II. CHLOKO PLASTIDS. 



Examine the chlorophyll granules (see page 41) in the fol- 

 lowing material : 



(a) The parenchyma cells of any thick leaves, for instance 

 those of Purslane, Begonia, etc., noting in the drawing the rela- 

 tive size and abundance of the granules in different cells. 



(6) The epidermis of the same leaves, noting in what cells, if 

 an}', the granules are found. 



Examine also the green bodies in the leaves of any true moss, 

 and in an}- filamentous alga, e. g., Spirogyra, and the cotyledons 

 of the following seeds for any green granules : sunflower, maple, 

 and pine. 



Raise three seedlings of flax and pine. Let one of the seed- 

 lings of each be kept in darkness, to the second seedling of each 

 give only a very little light, to the third give as much light as 

 possible ; and when the plumules have begun to develop, examine 

 the cotyledons and young stems for any color-granules. 



Do well-blanched celery petioles contain chlorophyll? To 

 answer this, examine the base, middle, and summit of the leaf- 

 stalk. 



The next three studies can be advantageously deferred until 

 after that of starch. 



III. LEUCOPLASTIDS. 



These bodies (see 174) require for their detection very careful 

 manipulation, but by following the directions given on page 44 

 they can usually be made out without much difficulty. For the 

 pseudo-bulb of Phajus, which is there recommended, the same 

 organ in almost any of the cultivated exotic orchids may be 

 substituted. 



IV. CHROMOPLASTIDS. 



These can be examined in any of the colored fruits; for 

 instance, in winter, the berries of Solanum Pseudocapsicum 

 (Jerusalem Cherry) may be used (as directed in 498). The 

 granules there found should be compared with colored granules 

 in the petals of almost any flower. For examination of the color- 

 granules in flowers, common pansies answer very well (see 477.) 



