210 THE AMERICAN NATURALIST. [VoL. XXXIII. 
Pror. D. T. Mac DoucaL: Symbiosis and Saprophytism. — It is 
customary to designate all chlorophylless, seed-forming plants, which 
have no nutritive connection with other vascular species, as sapro- 
phytes, or more exactly as holosaprophytes (allotropic or heterotropic 
forms, according to Pfeffer’s classification), and others of similar physi- 
ological tendencies as hemisaprophytes (mixotropic forms), without re- 
gard to the nutritive unions formed by the roots or absorbing organs, 
as in mycorhiza, tubercles, and other associations. It is obvious that 
the terms saprophyte and holosaprophyte should be applied to those 
species only which derive their food supply from organic products 
directly without the activity of chlorophyll and unaided by other 
organisms. In this sense, which appears to be the only meaning 
admissible, the holosaprophytes include numerous bacteria and fungi, 
but, so far as previous investigations show, only one seed-forming 
genus, Wullschlegelia. As the result of some work now in press, the 
waxy white orchid of the northwest, Cephalanthera oregana Reichenb., 
should be added to this category. 
As a consequence of the acceptance of the limitation of the term 
holosaprophyte, as given above, all those species furnished with 
mycorhiza or tubercles, or which enter into direct mechanical or 
nutritive associations, must be classed as symbionts. 
It is a matter of common knowledge that séedlings are holosapro- 
phytic in the stage in which they are wholly dependent upon the 
reserve material in the endosperm, and, in general, during the period 
previous to the formation of chlorophyll. This period is practically 
obliterated in those species in which chlorophyll is formed in the 
seed. The capacity for the absorption of humus products has played 
an important part in the production of the minute seeds of the orchids 
and other groups of similar physiological organization, and the exten- 
sion or retention of this capacity throughout a greater or less portion 
of the life of the sporophyte has resulted in varying stages of true 
saprophytism. Although, so far as known, this period has been 
extended to include the complete life history of this generation in 
only two seed-forming genera, the results of recent investigations 
show that practically all green plants are capable of taking up and 
using a varying proportion of humus products. Only those which 
show a marked extension of this capacity should be classed as hemi- 
saprophytes. The hemisaprophytes among seed-forming plants would 
therefore consist chiefly of carnivorous species, whereas nearly all of 
those now included are, in fact, more or less symbiotic by means of 
mycorhiza, tubercles, etc. 
