Box— Vol. I.] CAMPBELL— A^A/AS AND ZANNICHELLIA. 5 



development and histology of the reproductive parts of the 

 plants, as the general structure and histology of the vegeta- 

 tive parts has already been, on the whole, accurately de- 

 scribed; nevertheless, it has been found necessary to correct 

 a few points, the most important being the structure of the 

 vascular bundle of Naias. The absence of tracheary tissue, 

 which has been supposed to be characteristic of this genus^ 

 it is found is only apparent, at least in N. jlexilis, the only 

 species studied. Here tracheids are always found in the 

 young bundles, but are subsequently destroyed by the great 

 elongation of the parts, so that in the fully developed bundle 

 no trace of them is to be found. This will serve as one 

 more instance of the importance of studying the develop- 

 ment of the parts as well as their structure when fully 

 formed. 



Most of the results here given were obtained from the 

 study of serial microtome-sections. The material was in 

 most cases fixed with one per cent, aqueous solution of 

 chromic acid, and after thoroughly washing was transferred 

 gradually to alcohol, where it remained until wanted. No 

 other reagent employed gave as good results as chromic 

 acid, although material so fixed, unless very thoroughly 

 washed, is apt to offer resistance to nuclear stains. The 

 material was stained in toto with Czokor's alum-cochineal, 

 and after dehydrating was imbedded in parafiin. The earlier 

 preparations were passed through turpentine before imbed- 

 ding, but later xylol was substituted with excellent results, 

 the formula being that given by Zimmermann (1893, p. 

 33), except that a much shorter time than he gives was 

 found to be sufficient. The series of sections was after- 

 wards stained on the slide with a solution of Bismarck brown 

 in 70 per cent, alcohol. In the study of the embryo-sac 

 of Naias, the anilin-safranin method recommended by 

 Schaffner (1896, p. 123) was used to some extent and with 

 good results. 



•While Magnus denied the presence of tracheary tissue, he refers to the work of an 

 Italian, PoUini, who claims to have seen it. 



