OF ARTS AND SCIENCES. 113 



The wall of the frond, or cortex, and the diaphragms, are each com- 

 posed of a single layer of cells very similar in size and shape. In 

 shape these cells are somewhat flattened on their free sides, while 

 those portions in contact are polygonal. Of the three dimensions of 

 the cell, the one at right angles to the layer is the shortest in the 

 adult cells of both the diaphragms and the cortex. In the older cells 

 of the cortex the longitudinal diameter tends to become the longest. 

 Towards the tip of the plant, the radial diameter of the cells of the 

 cortical layer does not decrease much until very near the apex, but the 

 other two diameters decrease more rapidly, so that the cells become 

 columnar (Fig. 2). The whole plant is covered with an apparently 

 gelatinous cuticle, and the chambers contain what appears from alco- 

 holic material to be a viscid fluid. It becomes hardened in alcohol, 

 and is easily stained. 



All this is by way of introduction to a more careful examination of 

 the tip of the plant, which it will be necessary to make in order to see 

 just how growth takes place there, and to discover, if we can, how the 

 cells of the cortex and of the longitudinal filaments arise, and what is 

 the origin of the bulb-cells and of the diaphragms. The material that 

 I used in my attempt to answer these questions was collected by Dr. 

 Farlow at Wood's Holl, and preserved in moderately strong alcohol. 

 From the smallness and delicacy of the object to be studied, and the 

 consequent difficulty of making free-hand sections, it was evident that 

 nothing more was to be discovered by that means than what I have 

 already described. I therefore attempted to apply the methods now 

 in use by all animal histologists, of imbedding in paraffine and section- 

 ing with the microtome into ribbons. As the tissues of this plant 

 contain larger cavities with comparatively very thin walls my chief 

 difficulty was to get this tissue into the paraffine without allowing it 

 to collapse. Another difficulty was that when I stained with aniline 

 colors they would become washed out during the subsequent manipu- 

 lation. 



Both difficulties were avoided quite successfully in the following 

 manner. My material was put into 70% alcohol. From this, por- 

 tions that I wished to section were transferred to 90% alcohol to 

 harden. After being hardened, the specimen was stained. If it was 

 to be stained with some coal-tar color, I used a very strong solution 

 in 90% alcohol. If I wanted to get a hematoxylin stain, I trans- 

 ferred the specimen back to 70% alcohol and used Klemenberg's 

 method, or, more frequently, this method with the calcium chloride 

 omitted. After remaining in the stain about forty-eight hours, if the 

 vol. xxin. (x. s xv ) 8 



