K.— BOTANY. 177 



Kingdom, and I shall have something to say on that point anon, they 

 represent the most elementary types of holophytic plant-life to which 

 we are likely to have access. The probability that such forms will ever 

 be found preserved in the fossil state in sufficient numbers and showing 

 the necessary details of cell-structure to be of any value for comparative 

 morphological study or for the elucidation of the mode of origin of the 

 multicellular plant, appears at the best to be remote. A study of fresh- 

 water Algae is, therefore, one of fundamental importance, not only because 

 they illustrate various stages in the elaboration of a plant-body and 

 afford some rough picture of the early beginnings of plant-life, but because 

 it is in such unspecialised types that many important physiological problems 

 have found and will find solution. From this point of view the absence 

 of adequate facilities in this country for the direct investigation of these 

 forms on the spot is much to be regretted. 



The relation of the different types of construction, that can be dis- 

 tinguished among the lower Protophyta, to one another and to the more 

 elaborate parenchymatous soma usual in land-plants must always remain 

 in part a matter of conjecture. There are, however, certain definite 

 facts which emerge from a comparative study of the simpler holophytic 

 organisms and that have an important bearing on these problems. It is 

 with these that I shall more particularly deal in the first place. 



Parallel Evolution among Protophyta. 



It is now nearly thirty years since the doctrine of the flagellate origin 

 of the Algae became firmly established by the discovery in Sweden of 

 Chloramoeba and Chlorosaccus. These two simple forms agreed with a 

 number of others, already previously distinguished as Confervales by 

 Borzi 1 and Bohlin 2 , in a series of sharply defined characteristics, namely, 

 the possession of yellow-green, commonly discoid chloroplasts containing 

 an excess of xanthophyll and devoid of pyrenoids, the storage of the 

 products of photosynthesis in the form of oil, and the possession of a 

 motor apparatus consisting of two very unequal cilia attached at the front 

 end. These and other minor characteristics served to separate out from 

 the extensive group of the Chlorophyceae a small set of Algae which 

 became known by Luther's name, Heterokontae. 3 The large remainder 

 of the Chlorophyceae were renamed Isokontae, a designation based 

 upon the fact that here the motile stages bear equal cilia (commonly 2 or 4) 

 arising from the anterior end. In the Isokontae the chloroplasts are 

 often large and few in number and are commonly provided with pyre- 

 noids ; they contain the same four pigments as do those of the higher 

 plants and, so far as we know, in roughly the same proportions. Most 

 Isokontae, moreover, store their photosynthetic products in the form 

 of starch. 



Subsequent to this Blackman and Tansley in 1902 4 performed a 

 valuable service in issuing a revised classification of the Green Algae in 

 which the two classes, Isokontae and Heterokontae, were clearly distin- 



1 Slud. algol. Palermo, II, 1895, p. 99. 



2 Bih. K. Sv. Vet.-Akad. Handl. xxiii, Afd. 3, No. 3, 1897. 



3 Ibid, xxiv, Afd. 3, No. 13, p. 17, 1899. 



4 New Phytol. i, 1902, p. 17 et seq. 



1927 N 



