330 The Botanical Gazette. [June, 
On submerged sticks in ponds and ditches, vicinity of Cam- 
bridge, Mass. 
This Species is not uncommon about Cambridge, but I 
have never found it growing in any very great abundance. 
It almost invariably produces oospores and its androgynous 
character is constant. It differs from S. Reinschit in its 
smaller habit, in the modification of its exospore, which, ahi 
ever, is not always very pronounced, and especially in t = 
origin of its antheridial branch which in the last a : 
species always arises at a distance from the oogonium, er 
that has been established by the examination of abundan 
material collected about Kittery Point. 
arvard University, C. ambridge, Mass. 
EXPLANATION OF PLates XXI-XXIII. 
Rhipidium americanum Thaxter. 
ichot- 
Fig. 1. General habit of a more typical plant, the basal sinh 
omously thrice-lobed, the filaments showing occasional segm¢ th 
Fi eneral habit of a much branched specimen bearing 
oogonia and zoosporangia. €, 
Fig A Futlistety Prarhed depauperate plant seen from abov 
the zoosporangia not yet mature. : avout 
Fig Lobe of a depauperate plant with mature filam . cowine 
ig. 5. Portion of the margin of the lobe of a basal Acie nt bear: 
the origin of several filaments and the whole of a single fila 
three sporangia, two of them empt 
1g. 
Fig. 7. Z 
the papilla of dehiscence have been formed : wid 
Fi porangium killed at the moment of dehiscence. ica fe, 
a portion ot te spore mass extruded, surrounded by its en 
terminated by the papilla of dehiscence. e en- 
ig. 9. ehiscent pct tes just before the rubs fe me pa- 
velop surrounding the spore mass which is still terminated by 
pilla of dehiscence. broken at 
Fig. ro. meamoment later. The envelop = dehiscence 
the right allowing the zoospores to escape. The papillao 
is out attached to the envelop. ie 
Ta wi oospores, the lowest in dorsal view. : e ex0- 
Fig. 12. Gusentun: the periplasm in process of forming th 
spore. 
Fig. 13. 
view. : ical section. 
Fig. 14. Mature Oospore in oogonium, seen in optical depaupe 
Fig. 15. An abnormal form of sporangium common in 
ate individuals, 
w 
: ce 
. : in surfa 
Mature oospore in oogonium, the former seen 
; 
: 
4 
