ORCHIDACE^ 



anterior wall of the sac and their form maybe seen, in many cases, 

 through the translucent lateral walls. In the separation of critical 

 species I have found that these emergences or thickened tissues 

 are really helpful, often decisive. 



The sac of Erythrodes species is usually provided with three 

 conspicuous nerves that pass down the posterior wall and as- 

 cend by way of the anterior wall to the elongated limb of the 

 labellum. Alternating with these nerves are the carinae or pa- 

 pilliform calli just mentioned. They are usually four in number 

 when they occur, but in some species two may be suppressed, or 

 they may be broken up into cylindrical processes. Occasionally 

 the outer ones, those situated on each side of the lateral nerves, 

 are wanting; when present they are situated higher on the wall 

 of the sac than the inner ones. The central pair, one on each side 

 of the central nerve, may extend almost to the base of the sac 

 as thickened lines, or they may be for the most part suppressed 

 and appear simply as scale-like or papilliform calli, or, as in Ery- 

 throdes mexicana Ames, they may be verruciform. It is note- 

 worthy that these raised thickenings are not situated on the 

 nerves as is usually the case with such structures, but arise from 

 the interneural tissues. 



I have observed that in some species, as for example in Ery- 

 throdes vaginata (Hook.) Ames and E. querceticola (Lindl.) 

 Ames, there are prominences alternating with the nerves of the 

 sac, while in E. secunda Ames, there may be twelve cylindrical, 

 slender processes, that resemble hairs found in some species of 

 Goodyera. Four of these processes occur in a vertical line on 

 either side of the central nerve and two on each side of the sac 

 just below the point where the lateral nerves curve sharply up- 

 ward in their course. In other words these twelve processes in E. 

 secunda, six to the right and six to the left of the centre of the 



