MacMillan : Observatioxs ox Nereocvstis 295 



to Mr. Harold Lyon for assistance in the tedious routine of mi- 

 crotomy. The drawings were made by Miss Tilden under my di- 



,> 



rection. 



Hxplaualion of Pla eH. 



Plate 361 



Fig. I. riant .1 mm. in lengtli. Shows primary differentiation of holdfast and 

 stipe-laminar region. Enlarged. 



Fig. 2. riant I mm. in length. Stipe is already elongated. Tip of lamina is re- . 



moved. Enlarged. 



Fig. 3. Three young plants, eacli one-half natural size. The smallest was 6 mm. 



in length, the next 18 mm. and the largest 4.5 cm. These plants show the early rapid 

 enlargement ol" the laminar area. 



Fig. 4. A plant 14 cm. in length, reduced one-half, showing the origin of the 

 first c'eft near the base. The stipe is proportionally undergoing more rapid elongation 



in this stage 



Fig. 5. Pneumatocyst and laminar bases from a plant 50 cm. in length. Re- 

 duced one-half. Showing huw only the first cleft reaches the surface of the pneuma- 

 tocyst. 



Fig. 6. \'ertical section of primary fixation-area, showing rhizoid cells. From 



plant 18 mm. long. X 335* 



Fig. 7. Diagrammatic cross section of stipe. Sieve-tubes represented as dots. 



Plant 12 cm. in length. X 25. 



Fig. 8. Diagrammatic cross section through pneumatocyst of plant 12 cm. in length. 

 Plack spaces in central cylinder represent clefts in the gelatinous matrix, X 2$. 



Fig. 9. Diagrammatic cross section through base of primary lamina. Plant 12 cm. 



in length. X 25. ^| 



Fig. 10. Cross section through pneumatocyst of 12 cm. plant. Peripheral region. 



X335- 



Fig. II. Cross-section through pneumatocyst of 12 cm. plant. Sieve-tube re- 

 gion- X335- 



Fig. 12. Diagrammatic cross section of lamina in iS mm. plant. Mucilage ducts 



and jrrooves are indicated X ^5' I 



Fig. 13. Detail of laminar structure. Cross-section 25 mm. above the top of the 



I t 



pneumatocyst in 12 cm. plant. X 335- 



1*1. ATE 362 



Fig. 14. Cross section through base of lamina in I2 cm. plant showing groove, 

 which initiates the longitudinal division of the laminae. 25 mm. above top of pneu- 

 matocyst. X335- 



Fig. 15. Cryptostomatal area. Cross section immediately alx)ve pneumatocyst 



of plant 12 cm. in length. 



Fig. 16. Sieve-tube from stipe. 12 cm. plant. Shows the fragmented nuclei in 



the capillary cavity of the cell. X 335' 



Fig. 17. Trumpet-hypha from pith-web of plant 12 dm. in length. Shows gela- 

 tinous thickening of inner wall. X 335- 



Fig. 18. Origin of sieve tubes. Longitudinal section through area bounding the 

 pith-web. Plant 12 cm. long. Cells to the left with several nuclei become passively 

 elongated into the sieve- tubes. X 335* 



