2626 



Journal of Applied Microscopy 



suddenly from the form with spreading leaves to the flattened condition, and the 

 flattened branches again revert to the form with spreading leaves. 



1. Sketch a pine seedling which has sprouted, showing the seed coat still 

 covering the cotyledons. Sketch a seedling with cotyledons expanded. Describe 

 the important changes which take place in the embryo during the process of 

 sprouting. 



2. Sketch a branch of Juniperus communis and note that all of the leaves 

 are of the spreading type. 



3. Study and sketch the seedlings of Thuja occide?italis and note that at first 

 the leaves are of the spreading type, much like those of Juniperus, and that 

 later the branches have the flattened form characteristic of the adult plant. 



Fig. lo. — Diagram of life cycle of pine. 



Apply the recapitulation theory as given in connection with the moss protonema. 

 From this it would appear that the ancestors of Thuja had the leaves arranged 

 like those of the common juniper. 



4. Study and draw a small branch of Thuja (retinispora form) in which the 

 upper part of a flattened branch has changed back to the juvenile form. In 

 such cases there is a double reversion. In other words, the branch takes on 

 first one form and then another successively. 



5. Make a diagram showing the life cycle of a pine. See Fig. 13. 



6. Note on the development of the carpellate pine cone. 



The young carpellate cones of Finns laricio begin to develop in the bud 

 during summer or fall, and in the following spring the carpels have young ovules 

 with a distinct integument. Later the ovules are pollinated and the megaspore 

 is developed. In the following autumn (October) the megaspore has germinated 

 and the female gametophyte is developing as a hollow spherical body composed 



