430 BOTANICAL GAZETTE [MAY 
and latter parts of the summer, when the surface soil is no longer 
saturated with water, such annuals as Panicum capillare, Echi- 
nochloa Crus-galli, Eragrostis hypnoides, Stenophyllus capillaris, 
Polygonum Persicaria, Amaranthus paniculatus, and Erechthites 
hieracifolia take possession of all exposed surface soil and become 
exceedingly abundant. Much of the surface soil that has been 
denuded by burning or by other causes is already occupied, how- 
ever, by the rhizomes of perennials such as Ludwigia palustris, 
L. polycarpa, Proserpinaca palustris, etc. In these cases Bolionia 
Fic. 8.—a, Bolionia asteroides; b, Penthorum sedoides; c, Proserpinaca palustris; 
d, Ludwigia palustris; e, Callitriche palustris; July. 
asteroides, Callitriche heterophylla, and C. palustris are often abun- 
dant; both species of Callitriche, however, die away in midsummer, 
becoming replaced by annuals. Fig. 8 shows such a community. 
Callitriche, maturing earliest, is “seasonally” (WoopHEAD 18) 
complementary with the other species. Boltonia roots lowest, 
while its aerial shoot grows much the highest; and since it is not 
harmed very much by Proserpinaca, Ludwigia, and Penthorum, 
while they derive, if anything, benefit from its shelter, Boltonia 
is complementary both aerially and subaerially. Proserpinaca, 
