260 PROCEEDINGS OF THE AMERICAN ACADEMY. 



my own observations as to the fate of these nuclei do not entirely cor- 

 respond with Rosen's view, there remains something to be said about 

 them. The cells which are first cut off from the basidia are not the 

 spores themselves, for from their proximal end is always cut off a 

 small usually wedge-shaped cell (Fig. 6, «, b) the interstitial cell of 

 De Bary. The larger upper cell becomes the spoi'e, the small lower 

 one eventually disappearing. 



In the basidia there are always two and often more nuclei. When 

 a spore mother cell is about to be cut off one of these migrates to the 

 tip and there divides, a septum is soon formed below it, and the spore 

 mother cell is formed. Rosen states that when the interstitial cell 

 is about to be cut off, each of these twin nuclei divides, and from the 

 four daughter nuclei so formed two migrate to the lower end of the 

 cell, where they are cut off, and the other two remain in the spore 

 proper. In my own observations in by far the majority of cases the 

 nuclei separated without dividing, and were separated as single nuclei, 

 one in the spore and one in the interstitial cell (Fig. 6, a). The 

 nucleus in the spore always divided at least once, — in a considerable 

 number of cases, indeed, three nuclei were seen in the ripe spores 

 (Fig. 5, b, c), — while the nucleus in the interstitial cell sometimes 

 divided, but quite as often remained single, as long as the interstitial 

 cell persisted. As the sjjore ripens, the wall thickens and becomes 

 rough, the interstitial cell disappears, and the spore may be said to be 

 mature. The double nucleus remains quite distinct in the spore to 

 the oldest stages. 



In speaking of the double nuclei in the spore it should be men- 

 tioned that they are found in all of the other parts of the recidia, in 

 the hyphne, the pseudo-parenchyma, and the peridium. This ubiquity 

 tends to deprive them of so great a significance as some authors have 

 placed upon them. 



It is not necessary to follow the development of the tecidium any 

 further, the final rupturing of the peridium, etc. having been often 

 described in other forms. 



-^CIDIUM ON HOUSTONIA C^RULEA. 



Most of the material used for the examination of this species was 

 collected by Professor Thaxter, who kindly allowed me free use of 

 it. A small amount collected by myself at Sharon, Mass., was killed 

 in picric acid, and was valuable for some of the younger stages. This 

 aecidium is found both on the leaves and corolla of its host. The 



