78 Ilhodora [April 



I have referred above to the difficulties experienced in distinguish- 

 ing SpiraJithcs ccrnua from the variety ochrolcuca. Sometimes plants 

 that grow in upland meadows or in woodlands are arbitrarily referred 

 to the variety while the plants of boggy ground are referred to the 

 species. If a more reliable guide to differentiation is asked for we 

 find few collectors who are able to give it. There is only one sure 

 guide that I have found satisfactory, namely, polyembryonic seeds 

 for the species and normal seeds for the variety. This distinction 

 holds good in New England, at least, and may prove generally applic- 

 able. Usually a raceme in which the three lowermost flowers have 

 withered furnishes ovules that are in good condition for examination. 

 If the ovules are transferred to a slide, cleared with potassium hy- 

 droxide, rubbed under a cover-glass and then gently heated until 

 ebullition begins, the presence or absence of polyembryony may be 

 readily determined by means of the compound microscope. As a rule 

 the seeds of the species are balloon-shaped while the seeds of the vari- 

 ety are slenderly elliptical. A few comparative studies will soon 

 make clear when polyembryony is present. The difference, of course, 

 between the species and the variety is best observed in the contents of 

 mature capsules. As the plate (127) tends to show, there are slight 

 differences between the lips of the species and the variety. The lip 

 of the species is rather oblong, sometimes slightly constricted near 

 the middle; the nectar-glands are usually shorter than in the variety. 

 In the variety the lip is ovate or ovate-oblong in outline with the 

 glands slightly longer and perhaps more curved than in the species. 

 These characters, however, are not always so clearly shown as in 

 the plate and one form of lip may pass by imperceptible degrees 

 into the other. The only reliable distinction is found in the seeds 

 and it would be well worth while to ascertain by cultural experiments 

 whether or not this is due to the nature of the soil in which the plants 

 grow and whether or not it prevails throughout the range of the species. 

 Will the variety, for example, exhibit polyembryony if grown in bogs? 

 Will the species produce normal seeds if transferred to upland woods? 



Polyembryony was first demonstrated in Sjnranthes ccrnua by 

 Leavitt 1 in 1900, as a result of observations made in my laboratory 

 on specimens collected at North Easton, Mass. At first the occur- 

 rence of polyembryony was thought to be local as Curtis 2 had figured 



1 Rhodora, ii (1900) 227. 



2 Bull. Torr. Bot. Club, xx (1893) 188. 



