CHAPTER II. — PLANT TISSUES. 171 



form elongated and regular passages, resembling the air passages 

 of aquatic plants, into which adjacent secretion cells pour their 

 contents, Fig. 434, or they may be short and regular or irregular 

 closed cavities. They may, like secretion cells, contain oleo- 

 resins, balsams, gum-resins or mucilage, and in some instances 

 their form and contents make them liable to be confounded with 

 laticiferous ducts. 



f**' Practical Exercises. 



1. Obtain in spring or early summer, when vegetative growth is rapid, 

 some filaments of Spirogyra ; examine them microscopically by daylight, and 

 note that the cells all appear well developed, and no signs of cell-division are 

 observable. This is because in these plants the cell division takes place in 

 darkness. Let the filaments remain in water in a dark room until after mid- 

 night ; then place them in 60 per cent alcohol, which will stop their growth 

 and kill the protoplasm. Now study them microscopically, and cells will be 

 found in all stages of division, some in which the nucleus has just divided, and 

 an annular protuberance on the interior of the cell wall (the beginning of a 

 cellulose septum) has made its appearance ; others in which the division is 

 nearly completed, and still others in which the separation into two cells is quite 

 complete, but the new cells have not yet attained their full growth. 



Make drawings of different stages in the process. 



2. Strip off a small portion of the epidermis from the middle or basal por- 

 tion of the leaf of a Lily (any one of the garden or wild lilies will answer), treat 

 it with 60 or 70 per cent, alcohol for an hour, then stain with Grenacher's 

 carmine or Grenacher's hematoxylin, permitting the tissue to remain in the 

 staining solution for some hours, then examine it microscopically? Cells will 

 probably be found in which the nucleus is separating into two, and others in 

 which the division is complete, a new and very thin cell-wall being formed 

 across the cell. 



3. Examine a drop of active brewer's yeast under a magnifying power of 

 600 or 700 diameters. Budding cells will be observed, with the buds in various 

 stages of development. Make drawings of some of them. 



Obtain a piece of porous tile ; place one end of it in a small dish containing 

 water. The portion not immersed will be kept moist by capillary attraction. 

 On this portion place a little yeast ; cover the whole with a bell jar ; keep in a 

 moderately warm place for a few days, and then examine the yeast. Some 

 cells will probably be found in which the protoplasm has broken up into several 

 small, rounded masses, presenting an example of internal cell-formation. 



The little red Cup fungus, Peziza coccinea, is not uncommon in our woods. 

 Make a thin, vertical section of the "cup" or hymenium of one of these plants, 

 and examine with a magnifying power of 300 or 400 diameters. Numerous 

 elongated cells, each containing a number of oval spores called ascospores, will 

 be observed. Some of the latter may be seen escaping from the top of the asci, 

 or mother cells. Draw one of the asci with its contained ascospores. 



