34 Setchell. — An Examination of the Species 
upon Sagittaria in abundance at Norwich, Conn., in the same 
locality with D. opaca. The Sagittariae were growing 
in about six inches of water. In August, 1890, it was found 
in Cambridge, Mass., in a ditch full of water near some 
brickyards. 
Cornuella lemnae, sp. et gen. n. 
This form inhabits the older fronds of Lemna ( Spirodela ) 
polyrrhiza , giving no sign of its presence except as the dying 
fronds, becoming more transparent, show the dark sori scat- 
tered through them. 
The mycelium is not very abundant and has nothing par- 
ticularly characteristic about it. The sori are found in the 
large intercellular chambers of the spongy parenchyma just 
above the lower epidermis. They have all the appearance of 
a Doassansia until examined in thin sections. They are 
rather small, being from 50 /x to 70 [i in diameter, but oc- 
casionally one is found measuring 100 jx across. They are 
nearly globular or decidedly ellipsoidal and are nearly black 
when ripe. 
The structure of the sorus forms the characteristic of the 
genus. The interior is composed of loosely interwoven fine 
hyphae (Fig. 82), which appear to be hardened and of a 
brownish colour. Surrounding this mass of hyphae is a 
compact layer of spores, which have the same general struc- 
ture as the Doassansia- spores. They are more or less oblong 
in cross-section, often somewhat elongated radially, and 10 n 
to 1 2 ju long by 6 n to iOju broad. There is no trace of a 
cortex, nor are there any external layers of hyphae as in most 
of the species described above. 
The development of the sorus resembles that of the rest 
of the Doassansia-gxovep in its earliest stages. The hyphae 
form an irregular, tangled ball in the air-space at first. The 
hyphae, however, soon seem to radiate in all directions from 
the centre, and the free tips appear swollen (Fig. 83). The 
spores are formed from these swollen ends and are separate 
when young, but as they mature they become compacted 
