740 MINNESOTA BOTANICAL STUDIES. 



5. Plant " B " of text; the midrib is more distinct and the two op- 

 posite growing points of the first pair of pinnae may be seen just be- 

 low the junction of lamina with stipe. 



PLATE LVIII. 



Plant " C " of text. The plant is shown a little more than one- 

 third the natural size. It presents the loosely arranged pinnae charac- 

 teristic of young plants and as shown in Ruprecht's plate. The lower 

 pinnae are perforated by marine animals and are the ones in which the 

 reserve material is the most abundant. The mid-lamina alone shows 

 a midrib. 



PLATE LIX. 



Plant " D " of text. The size is indicated by the hat placed in the 

 field of view. It is about one-tenth natural size and was photographed 

 on the shore a few moments after collection. It is somewhat fore- 

 shortened, being between three and four meters in length. The cen- 

 tral lamina is shown in line with the stipe. 



PLATE LX. 



Pinna-region of full-grown specimen, one-half natural size. The 

 very much crowded position of pinnae in old plants is indicated in this 

 plate. Below the pinnae may be seen scars left by pinnae of previous 

 seasons. 



PLATE LXI. 



Cross sections through the stipe, natural size. The lower figure is 

 taken near the base of the stipe, while the upper is cut just below the 

 region of pinnae. The great difference in the extent of the pith and 

 in its shape, in the two sections, is noticeable. The characteristic 

 rings of growth are apparent in both figures. 



Plates LVII. to LXI. are from photographs made under the direc- 

 tion of the author, by Mr. C. J. Hibbard, Photographer of the De- 

 partment of Botany in the University of Minnesota. 



PLATE LXII. 



The anatomical detail of Pterygophora. 



1. Cross section through secondary cortex of stipe, showing rings 

 of growth ( x 50). 



2. Cross section through stipe, showing secondary cortex above and 

 primary cortex below (x 50). 



3. Longitudinal section through secondary cortex showing flatten- 

 ing of cells towards the right. This would appear as a ring in the 

 cross section ( x 50). 



