222 



Methods in Plant Histology 



without any imbedding. It is easier to get good sections of L. lucidu- 

 lum and L. inundatum than of drier species, like L. obscurum and 

 L. clavatum. Safranin and DelafiekTs haematoxylin is a reliable 

 stain. Safranin with anilin blue or light green is also good, and the 

 light green gives particularly clear views of the phloem. 



This stem, though rather complicated and confusing to the begin- 

 ner, affords an illustration of the exarch protostele, the most primitive 

 type of vascular cylinder (Fig. 73). 



C'&'J '' . i 

 - -'. - 



1 



PIG. 73. Lycopoditim Billardieri, a New Zealand species: photomicrograph of trans- 

 verse section of stem; fixed in formalin alcohol, cut in paraffin, and stained in safranin 

 and anilin blue. From a preparation by Dr. J. Ben Hill. Cramer contrast plate; 

 16 mm. objective; no ocular or Abbe condenser; camera bellows, 1 meter; yellowish- 

 green filter; arc light; exposure, 5 seconds. X44. 



The strobilus. For longitudinal sections, cut a slab from each 

 side of the strobilus to insure fixing and infiltration. If a strobilus, 

 or similar organ, is simply halved, both pieces are likely to curve. 

 Among north temperate species, Lycopodium inundatum is the most 

 easily cut. A young strobilus 1 cm. in length may show all stages 

 from the archesporium to the spore mother cell. Iron-haematoxylin 

 is the best stain for differentiating the archesporial cells. The divi- 



