PTERIDOPHYTES— LYCOPODIALES 299 



Vegetative structure. — The short, thick stem, even in old plants, 

 cuts easily in paraffin. Fix in formalin acetic alcohol and stain in 

 safranin, gentian violet, orange; or in safranin and light green. 



Sporelings with stems about 2 mm. in diameter and young plants 

 with stems up to 5 mm. in diameter are best for a study of the peculiar 

 vascular system of this plant. These young stages fix well in chromo- 

 acetic acid and are not hard to cut. 



Sporangia. — All the sporangia of the plant may be said to constitute 

 a single strobilus of the Selago type. Both longitudinal and transverse 

 sections should be cut. The stem is so short that, in a plant of medium 

 size, a longitudinal section may include the stem, the sporangium, 

 and the sporophyll, up to the top of the ligule. Such sections, 10-15 ju, 

 or even 20 n, in thickness, are best for demonstration. Early stages in 

 the development of the sporangium should not be thicker than 5 /x and 

 should be stained in iron-alum haematoxylin. 



Transverse sections through the whole cluster of sporophylls show 

 the arrangement of megasporophylls and microsporophylls and also 

 the relations of the sporangia to sporophylls. 



The gameto-pJnjies. — The spores are shed in the uninucleate stage, 

 and consequently it is not so easy to find the germination as in the 

 case of Selaginella. When the large megasporangium begins to decay, 

 let the megaspores dry naturally. They retain their power of germina- 

 tion for a year at least. Simply wet them with tap water and the 

 earlier stages are easily secured, quite clean and ready for cutting. 

 There must be soil in the dish for later stages. Try a similar method 

 for microspores. Also, look at the top of the stem of old plants for 

 stages developing naturally. The cell walls of the male gametophyte, 

 as in the case of Selaginella, are rather hard to differentiate. Use anilin 

 blue or light green. 



