Laing. — On the Classification of the Algae. 801 



(4th.) The Confervacea are widely separated from the Hphzro- 

 plea by both Sachs and Bennett ; but these two orders differ 

 only in their mode of reproduction, whilst they closely resemble 

 each other in general structure and appearance. 



It seems to me that the principal cause of error in these two 

 classifications is the idea that all the Oospore?, must be closely 

 related, for behind this idea is the belief that fertilization has 

 arisen only once in the vegetable kingdom ; that is to say, that 

 all plants which are reproduced by fertilization are descended 

 from a common stock. But this scarcely appears to me to be 

 correct, for fertilization has evidently arisen independently in 

 the animal and vegetable kingdoms, as it is not found in the 

 Protozoa, or the Palmellaceee, the lowest divisions of each king- 

 dom. Again, looking at the Alga themselves, we see that 

 fertilization is not the same process in all. The oospheres of 

 Fucus, for example, differ considerably from the oospheres of 

 Vaucheria ; but, at tbe same time, the structure of the stem in 

 the two genera is totally dissimilar. Now, it is much easier to 

 suppose that fertilization has arisen independently in these two 

 groups, than that they have diverged from a common ancestor, 

 reproducing itself in this way. For it can scarcely be doubted 

 that fertilization first originated in conjugating zoospores. We 

 have only to suppose (and the supposition is perfectly warrant- 

 able) that an advantage was gained by a specialization of the 

 functions of the two cells ; the one increasing in size and 

 becoming passive, the other remaining small and motile, since 

 it would have to penetrate into the interior of its companion 

 cell. Through some such variation as this, fertilization might 

 easily have arisen on various occasions. 



One more objection might be taken to Sachs' classification of 

 the Alga. He has included the Characea under the Carposporea; 

 though it appears probable that they should stand by them- 

 selves. Perhaps they are degenerate forms of a higher type ; 

 for it is only in habit and, to some extent, in structure of stem, 

 that they at all resemble the Alga ; and we know that many fresh- 

 water plants have become much simplified in structure (e.g. Mar- 

 silia and many of the Naiadea). A plant living in water has no need 

 for a stem built up of many tissues. The simplicity of the stem 

 oi Chara does not necessarily therefore connect it with the Alga, 

 and its reproduction, on the other hand, can scarcely be com- 

 pared with that of the Floridea and Coleochatea. Professor 

 Sachs has endeavoured to trace out homologies between the two, 

 which, however, to me appear to be far-fetched and doubtful. 

 It is much easier to suppose that the Characea, is an order 

 standing by itself, than to consider it as allied either to the 

 Alga or the Musci. Mr. Bennett has well dealt with this 

 question in the " Journal of Botany," 1878, p. 202 ; so it will 

 not be necessary to go into any detail here. 



