410 Mr. Bowman on the Parasitical Connection 
am therefore inclined to believe that the pale and sickly hue of 
such parasites, whether fixed on roots or. stems, results at least 
as much from this circumstance as from the surreptitious nutri- 
ment on which they feed. The absence of true leaves consti- 
tutes one essential physiological distinction between Cuscuta and 
Viscum ; and though Listera Nidus avis, Monotropa, and Orobanche 
are parasitic on roots, they are also destitute of leaves furnished 
with pores. Allsuch plants are consequently incapable of draw- 
ing sustenance from the atmosphere, and of being acted on by 
the powerful stimulus of light, and can only derive the necessary 
supply of food through the medium of their lower extremities. 
It may be said that as they find their food ready provided for 
them by the stock on which they grow, leaves would be super- 
fluous ; and that Nature, in depriving them of these usual organs 
of assimilation, has, in the plenitude of her power, prepared it 
for them through the medium of a foreign source. But this 
does not explain the cause of the absence of green colour; in- 
deed the instance of the Misletoe renders the reasoning incon- 
clusive. This plant is perhaps more strictly parasitical than 
any of those just named, yet it is green ;—a necessary conse- 
quence, as I conceive, of having leaves, though they be sparingly 
supplied with pores *. 
I hope to make it appear that the Lathrea differs in struc- 
ture from all the parasites just named ; and that, though it be 
* I have observed that the Misletoe dies with the tree on which it grows; and from 
a notice in the Magazine of Natural History (vol. ii. p. 294.), it seems that the La- 
threa does so too. It has long been doubted whether Listera Nidus avis be strictly 
parasitical. Whatever it may be in the earlier stages of its growth, it certainly is not 
so in its more advanced state. If it be carefully got up in a clod, and the soil after- 
wards washed from around it, the base of the central root or caudex may be seen to 
terminate in a short curved spur, which tapers to a fine point, and evidently is not at- 
tached to any other vegetable. The cuticle of the stem and its bracteas has no per- 
spiring pores. 
| parasitic 
mr ar atrii io it is io o DAR diii e. 
