EXPLANATION OF PLATES. 29I 



Plate; XXXIII. 



Fig. 54. Potamogeton pectinaius , ^igarAiciorra oi Dudley, sprouting tuber, ij< times natural size. 

 Aquarium, Februar>-. 



Fig. 55. Potamogeton peciinaius, gigantic form of Dudley, tuberous runner, natural size. 



Fig. 56. Potamogeton pectinatus, spray, showing cases of chironomids, nattiral size. September- 

 November. 



Fig. 57. Potamogeton Robbinsii, characteristic vegetative structure, rooting at nodes, iji times 



natural size. May. 



Plate XXXIV. 



Fig. 58. Potamogeton amplif alius , rooted tip of branch, a propagative structure. April. 



Fig. 59. Potamogeton crispus, germinating burs. October. 



Fig. 60. Potamogeton crispus, burs in various stages of development. June. 



Plate XXXV. 



Fig. 61. Potamogeton pectinatus, gigantic form of Dudley, erect axis of plant, 5 feet 2 inches tall, 

 bearing runner at base of stem. November. 



Fig. 62. Potamogeton pectinatus, gigantic form of Dudley, portion of leafy spray showing tubers. 

 November. 



Plate XXXVI. 



Fig. 63. Potamogeton obtusifolius, winter huds. October. 



Fig. 64. Potamogeton obtusifolius, erect axes bearing winter buds. October. 



Fig. 65. Potamogeton zosterifolius, sprouting winter bud. Aquarium specimen. February. 



Plate XXXVII. 



Fig. 66. Potamogeton pectinatus , cross section through stem, showing numerous air spaces. 



Fig. 67. Potamogeton Robbinsii, branch, showing points where dismemberment occurs, i, 2, 3. 



Fig. 68. Potamogeton Robbinsii, branch defoliated by larvEe of Nymphula sp. {Paraponyx). Larval 



cases, I, 2, 3. 



Plate XXXVIII. 



Fig. 6g. Potamogeton Robbinsii, photo-micrograph of section through old stem, showing arrange- 

 ment of mechanical tissue. 



Fig. 70. Detail of fig. 69. 



Fig. 71. Potamogeton crispus, photo-micrograph of section through stem of starch-filled vegetative 

 structure: a, cell with starch grains. November. 



Plate XXXIX. 



Fig. 72. Potamogeton crispus, leaves, showing characteristic leaf mining of chironomids. 



Fig. 73. Potamogeton amplif alius, leaves, showing characteristic mines of Hydrellia sp.; a, b, pupa 

 cases at end of mines. August. 



Fig. 74. Potamogeton amplifolius; a, b, leaves, showing circular pieces cut away by larva of Nym- 

 phula sp. (Paraponyx); i, larva in case; c, dead leaf, showing cases of Chironomus sp. 



Fig. 75. Potamogeton americaniis , spray showing attachment of cases of caddis fly (fam. Leptoce- 

 ridse); a, case of caddis fly; b, stipule of leaf. June 31, 1914. 



