THALLOPHYTA 359 



must not be taken for more than they are worth, since they raise 

 questions which cannot be definitely answered. Nevertheless they 

 are worthy of consideration as giving a point of view which will 

 have its value in directing the study of the lower organisms, whether 

 of the Animal or of the Vegetable Kingdoms. 



The instability of nutritional method in Euglena — and especially 

 its mixed nutrition, partly photosynthetic and partly saprophytic, as 

 it grows strongly in foul water — finds its parallel in the mixed nutrition 

 of many land-living Plants. It seems probable that irregular nutrition 

 has been widespread, from very low forms such as Euglena to the 

 highest Flowering Plants (Chapter XII.). At various points in the 

 series the dependence upon physiological supply other than by photo- 

 synthesis may have been accentuated. The parasitic Seed-Plants, 

 such as Viscum or Cuscuta, and the saprophytes, such as Neottia or 

 Monotropa, are cases where it was adopted relatively late, in forms 

 with their character already stamped as Seed-Plants. The various 

 groups of Fungi are cases where the physiological dependence was 

 established early, but after the encysted state had been definitely 

 adopted. A similar segregation, but earlier still, with absence of 

 encystment, would account for the establishment of the Animal 

 Kingdom. 



Such suggestions as these are based upon the actual facts observed 

 in simple organisms referable to the Flagellatae. It may be uncertain 

 whether or no these forms were or were not like the original sources 

 from which Vegetable and Animal Life sprang. They serve, however, 

 to give some idea of the possible origin and early relations of the 

 larger groups of living organisms, and of their differentiation on 

 the basis of nutrition, and of certain fundamental features of their 

 structure. In point of habitat the significance of these comparisons 

 cannot be mistaken ; for all these organisms are either aquatic, or at 

 least they live where water is readily available. It has been concluded 

 from this general fact that Life, whether of Animals or of Plants, 

 originated in the water, and probably in the first instance in the water 

 of the ocean itself. This is the position here adopted as a Working 

 Hypothesis, to be accepted until it is disproved. In studying those 

 few selected examples of the Thallophyta which it is possible to 

 describe in this book, they will be held as illustrations of primitive 

 Plant-Life. But the members of any definite natural affinity may 

 be seriated, so as to illustrate progress from simpler to more complex 

 conditions, and so it may be found possible, upon a basis of comparison 

 — but always open to correction as new knowledge is acquired — 



