A New Hybrid Fern. 83 



green, 14 - 30-f urrowed and the ridges almost smooth; 

 central hollow very large, stem- wall very thin; sheath 

 elongated, slightly enlarged upward, marked with a black 

 girdle at the base of the teeth; teeth mostly deciduous, 

 white, marginal. — British Columbia to New York, south 

 to California, Texas and Georgia. 



8. Equisetum hyemale L. (Plate 4, Figs. 12, 13.) 



Common Scouring-rnsh . 



Stems slender, rather stiff, evergreen, 2-4 ft. high, 

 rough, 8 -34-f urrowed, seldom branching; central hollow 

 large, h~s the stem diameter; sheaths marked with 

 two black girdles; teeth brown, membranous, soon decid- 

 uous. Spikes pointed. — British Columbia to New 

 England, south to California and Georgia; Europe; Asia. 

 Formerly used for scouring floors. 



Explanation of Plate 4. 



Fig. l, Equisetum variegatum, cone and stem-tip, x l > fig. 2, 3, Equi- 

 setum laevigatum; fig 2, joint of stem with bract-leaves; fig. 3, cone, x U 

 fig. 4, Equisetum scirpoides, the left stem with bud-like terminal cone, the 

 right stem sterile, x IM« Ag. 5, 6, Equisetum Ulmatcia; fig. 5, a few joints 

 of the green vegetative stem; fig 5, the top of the whitish, fertile stem with 

 large bract-like leaves and cone, x X A\ fl g- 7 » Equisetum fluviatUe, upper 

 portion of stem, and cone, x Hi flg. 8, 9, 10, Equisetu m arvense; fig. 8, the 

 upper part of the green vegetative stem; fig. 9, the top of the whitish fer- 

 tile stem with large bracts and cone, x H; fig. 10, the side view of a sporo- 

 Phyll, x 2 3"3. fig. 11, Equisetum palustre, upper portion of plant and 

 cone, x Ml figs. 12, 13, Equisetum hyemale; fig. 12, a joint of the stem 

 with bract leaves; fig. 13, a cone, x *« 



A New Hybrid Fern. 



F. C. GREENE 



Polystichum acrostichoides x Dryopteris cris- 



tata hyb. nov. 



In general appearance the hybrid closely resembles 

 Polystichum acrostichoides. The fronds are dark green 

 above and paler beneath. The fertile fronds have con- 

 tracted pinnae in the upper spore-bearing portion as in 



