278 



METHODS IN PLANT HISTOLOGY 



Antheridia. — It is not difficult to get good preparations showing 

 the development of antheridia. In forms like Conocephalus, Preissia, 

 Pellia, etc., cut out small portions of the thallus bearing the antheridia. 

 The piece should not be more than 1 cm. long and 5 mm. wide, pref- 

 erably smaller. For the development of the antheridia of Marchantia, 

 select young antheridiophores which still lie close to the thallus. With 

 the antheridiophore, cut out a small piece of the thallus, about 5 mm. 

 in length. For general development, cut 5 /x, but, for details of sper- 

 matogenesis, sections should not be thicker than 1 or 2 /x (Fig. 79). 



Fig. 79. — Marchantia polymorpha: early stages in the development of antheridia; from an un- 

 published drawing by Dr. W. J. G. Land. X600. 



Sections should be stained in iron-alum haematoxylin. The cells 

 are very small and the contents very dense; consequently, the staining 

 must be very critical to show the blepharoplasts and chromosomes or, 

 in later stages, the transformation of spermatids into sperms. If the 

 material is perfectly infiltrated and imbedded, there should be no diffi- 

 culty in getting sections as thin as 1 m- We have never seen a rotary 

 microtome with which anyone except Dr. Land can cut a good ribbon 

 at 1 m; but the comparatively cheap sliding microtome, shown in 

 Figure 2, cuts readily at 2 /x; and a modified type, a little more ex- 

 pensive, with a wheel for 1 /x, makes even ribbons at 1 ju- With Griibler 



