THE SELECTION OF PLANT TYPES. 197- 



sents a great advance in complexity and the essential features 

 of that general reproductive type which characterizes the great 

 majority of plants. The masking of the chlorophyll by a sec- 

 ondary pigment, peculiar to so many marine Algae, is here well 

 shown. If distance from the seashore or other causes make it 

 too difficult to obtain this plant, it may be replaced by Vaucheria, 

 which grows in green mats in brooks and springs. Its oogamic 

 reproduction is as typical as that of Fucus, and it illustrates the 

 structure of the remarkable siphonaceous group of Algae, which 

 presents such complication of external form in tropical seas. 



4. BatracJiospermtim, common in flowing currents of fresh 

 water streams, shows the peculiarities of the red Algae in its 

 thallus, built up of branching filaments, and its spore-tufts, each 

 the product of a single sexual union. 1 Here is the basis for 

 all the extraordinary variations of thecarposporic type of repro- 

 duction which finds its culmination in this group. Equally 

 useful and almost identical in structure is the slippery iVema- 

 liou which covers many a bold rock that is uncovered at low 

 tide all along our coast, but rarely more abundantly than at 

 Wood's Holl and on the neighboring islands. 



Our list of Algae is complete without mention of the old 

 friend of many years and much searching, the stonewort, Chara. 

 It is impossible to see what conditions have determined the 

 survival of this feature of the original biology course for so 

 many years, except its ready accessibility in some regions and 

 the force of habit. Its vegetative structure and its reproduc- 

 tion are characteristic of nothing but the isolated little family 

 to which it belongs. Unique in almost every respect, and 

 highly specialized, these plants illustrate no important feature 

 of vegetable life in so characteristic a form as do many Algae, 

 with the exception of protoplasmic rotation, which is by no 

 means a general phenomenon. They throw no light on the 

 structure or relationships of other plants, and even their own 

 systematic position is doubtful, for they are hardly Algae, on 

 the one hand, or Bryophytes, on the other. It is quite time 



1 For our present purpose it is not necessary to discuss existing differences of 

 opinion as to the pliysiological necessity for the act of fertilization in some red 

 Algae. 



