194 PROCEEDINGS OF THE AMERICAN ACADEMY 



wards, will throw a considerable liglit on the changes of structure 

 which it has undergone in its previous development. In such a series, 

 projecting portions, such as A', etc., are of significance m showing 

 that the growth in complexity from the simple membrane did not 

 originate from one point and extend out regularly, but originated at 

 several points irregularly situated. A comparison between Figures 1 

 and 2 will also show this. 



To get these sections some series were made by hand with the 

 razor, and more complete ones were cut on a microtome from speci- 

 mens which had been embedded in paraffine. Some of the latter 

 were from specimens which had been treated with corrosive sub- 

 limate. They were stained with Kleinenberg's haematoxylin before 

 being embedded, and mounted in balsam after they were cut. Some 

 of the series gave very good results, others were very much shrivelled. 



The upper portion of the blade, or the primitive blade as it is con- 

 venient to term it, is but a single layer of cells thick, as appears in 

 sections as well as by focusing. As seen on the flat surface of the 

 blade the cells are nearly square or slightly rectangular, but in some 

 cases elongated in the direction of the long axis of the blade. In 

 transverse section they appear nearly as thick as broad, but they vary 

 much in this respect. The cells contain a number of large and con- 

 spicuous lenticular chromatophores, usually arranged about the inner 

 walls. The protoplasm in these cells is in the form of a thin film 

 lining the wall. The nucleus is nofvery conspicuous, and is hard to de- 

 monstrate. These cells possess all the characteristics of age, and have 

 probably ceased to take any active part in the growth of the plant. 



On the one-layered portion were found in some of the specimens 

 the small clusters of hairs already alluded to. Attempts to get a g^od 

 section through such a bunch were fruitless. As far as could be seen 

 by focusing, the hairs protruded only on one surface, and were gener- 

 ally five or six in number. AVhen viewed from the other side from 

 that on which they were situated, they were seen to arise from basal 

 cells formed from the divisions from one (or at times from two) of the 

 ordinary cells of this portion of the blade. The basal cells of the hairs 

 are almost isodiametric, are densely filled with protoplasm and chro- 

 matophores, and possess a single large nucleus. Farther up, the cells 

 become elongated in the direction of the long axis of the filament ; the 

 protoplasm becomes filled with large vacuoles; and the nucleus be- 

 comes central, and connected with the peripheral protoplasm by fine 

 threads. At the distal end the cells are four to six times as long as 

 broad, and are destitute of contents. These hairs accordingly have 



