124 THE GYMNOSPERMS 



Cycadales. Another very interesting group of the (jymno- 

 sperms is the order Cycadales which is mostly tropical in habit. 

 In this order we find the Cycas revoluta which is frequently 

 grown in greenhouses. Its chief point of interest botanically is 

 in the fact that it possesses many characters in common with the 

 ferns and forms a sort of connecting link between the Gymno- 

 sperms and the Pteridophytes or ferns. 



We all readily recognize the great value of the Gymno- 

 s perms. Many of them are among our most important forest 

 trees from which we derive enormous amounts of lumber for 

 building purposes and cabinet making. They also furnish our 

 commercial supply of turpentine, resin and balsams. The 

 cypress is used extensively for telegraph and telephone poles. 

 The use of evergreens for ornamental plants is directly con- 

 nected with the nursery business and landscape gardening and 

 involves very large expenditures of money. 



EXERCISES WITH (JY^IXOSPERMS 



1. Examine a number of evergreen trees and note their straight 

 shaft, mode of branching and general form. 



2. Growth and Leaves of Pines. Examine a pine tree and note 

 the long shoots that are produced each year. Also note the short shoot* 

 composed of clusters of needles. Count the needles in the clusters in tlu> 

 different kinds of pines that may be available. Is the number constant 

 for each species? 



3. Examine a needle carefully; make cross-sections by cutting the 

 needle in a bit of pith and examine under the microscope. Note the thick 

 cuticle, the thick epidermis, the sclerenchyma and the chlorophyll-bearing 

 parenchyma. 



4. Twigs of Cone-bearing Trees. Cut across radial and tangential 

 sections of a branch from a cone-bearing tree and examine under the 

 compound microscope and note the points referred to in the text. 



5. Cone Flowers. Examine young staminate and pistillate cones 

 and note the points, referred to in the text. (This material can be col- 

 lected in the spring and preserved in alcohol or formalin.) 



6. Pollen Grains. Examine some of the pollen grains under the 

 compound microscope. 



