148 TYPE STUDIES 



a few very large spores, megaspores. These two forms of 

 sporangia are termed respectively microsporangiaaxiA. mega- 

 sporangia, and the scales which bear them are m,icrosporo- 

 phylls and megasporophylls. Draw the microsporophylls 

 and megasporophylls, viewed from the inside, showing the 

 form of the sporangia. 

 3. Construct a diagram illustrating the attachment of the 

 two forms of scales to the axis of the cone and their 

 distribution above and below. 

 The scales, as stated above, are sporophylls differentiated into 

 two forms. What are the reasons why they should be so consid- 

 ered ? The differentiation of spores into two sizes, microspores 

 and megaspores, which develop respectively male and female 

 gametophytes, is called heterospory. 



C. The microsporangium and inicrospoi-es. Split a microspo- 

 rangium open and note the immense number of minute 

 •microspores. Draw, under h.p,, a portion of the wall of 

 the sporangium, showing the cell structure, and a group of 

 spores. 



D. The megasporangium and megaspores. Split a megasporavr 

 gium open and count the large m,egaspores. Is the number 

 the same in all sporangia? Draw a megaspore under h.p., 

 showing the form and markings on the wall. What is the 

 significance of the angles on one side ? Like the spores 

 of the bryophytes and pteridophytes generally, and also 

 like the microspores, they are developed in groups of four, 

 tetrads, from spore mother cells. Under the same magnifica- 

 tion draw a microspore by the side of the megaspore to 

 show comparative size; 



E. The cell structure, or histology of stems and leaves. 



1. Cut cross sections of the stem. Note the epidermis and the cortical 

 ground tissue surrounding two or more air spaces crossed by delicate 

 filaments. In the center of each space lies Sifibro-vascular bundle 

 consisting of a strand of wood (xylem) surrounded by bast (phloem). 

 The further examination of these elements in cross and lengthwise 

 sections may constitute a detailed study. 



