Januaey 15, 1909] 



SCIENCE 



95 



from the previous lines of evolution, and 

 this point of divergence is the actual origin 

 of the new phylum. As far as this idea 

 dominates, so far does the phylum extend, 

 and Avhen a still newer idea comes in and 

 attains dominance, a still newer phylum 

 has its beginning. 



In this manner may we mark the begin- 

 ning and the extent of phyla. They origi- 

 nate with a divergence which is the ex- 

 pression of a new idea. It is what we 

 often call a "tendency." In taxonomy we 

 refer to it as a "new character," this latter 

 term being sometimes somewhat confus- 

 ingly applied to the underlying idea and 

 sometimes to its obvious structural ex- 

 pression. 



The result of the successive develop- 

 ment of phyla is quite like that in a tree 

 where newer branches spring from, older 

 ones by the formation of buds, from which 

 branches develop in succession. And as 

 there are branches of all grades, from the 

 primitive diverging growths which event- 

 ually divide the tree profoxmdly into great 

 segments, through the smaller and smaller 

 branches to the very recent slender twigs — 

 the growths of but yesterday— so it is with 

 the development of successive phyla from 

 one another, the result being a complex 

 tree-like aggregation with older phyla 

 below and younger and smaller phyla 

 above. 



In order to discern phyla, the botanist 

 must certainly be familiar with the whole 

 vegetable kingdom, or at the least with the 

 great region in which the particular phyla 

 under consideration occur. He must be 

 able to bring to mind the families, genera 

 and species of plants with such clearness 

 as will enable him to see the direction of 

 the evolutionary current — the "drift" of 

 evolution in the vegetable kingdom as a 

 whole, and in the particular portion im- 

 mediately under his consideration. I 

 know that this is often a difficult task, just 



as it may be very difficult to determine the 

 direction of the water current in a lake by 

 observations at one point only: yet it 

 may be very easy when the points of ob- 

 servation are multiplied. So it is here 

 difficult, and perhaps impossible, for the 

 man whose point of view is limited to a 

 small portion of the botanical shore-line. 

 The trained eye of the experienced man can 

 catch the drift of the waters from a few 

 properly selected points of observation, 

 and likewise the trained eye of the botanist 

 from observations at properly selected 

 stations may detect the direction of evolu- 

 tionary progress, as well as the origin and 

 extent of the resulting phyla. 



Applying what has been suggested in the 

 foregoing brief and somewhat desultory 

 discussion, it appears to me that we may 

 recognize the following plant phyla of 

 primary rank : 



1. Myxophyceae, in which the dominant 

 idea is the simple nucleus, typically not 

 limited by a nuclear membrane. The 

 simple plant body, of one or only a few 

 ceUs, the blue-green diffused pigment, and 

 the soft and often gelatinous walls may be 

 regarded as characters of secondary im- 

 portance. 



Here are included also many liystero- 

 phytes (bacteria) which I regard as de- 

 generates from the normal plants of this 

 phylum. 



Probably from the highest Myxophyceae 

 came the second phylum — 



2. Protophyceae, in which the dominant 

 idea is the definite nucleus, limited by a 

 nuclear membrane. The simple plant 

 body of one cell or of a repetition of mostly 

 similar cells, the typically motile, ciliated 

 gametes, the definite chromatophores carry- 

 ing a chlorophyll-green pigment, and the 

 usually firm cell wall, are limiting sec- 

 ondary characters. 



I here include Pleurococcaceae, Vlvaceae, 

 Ulotrichaceae, Oedogoniaceae, Coleochae- 



