September 30, 1898.] 



SCIENCE. 



429 



wanting we have no right to speak of a 

 a perennial succession of like individuals, 

 for it may be claimed succession means by 

 sexual genereration only. This interpreta- 

 tion is very convenient if one wishes to ig- 

 nore forms like bacteria and Saccharomy- 

 <3etes in the consideration of the question of 

 species, but to exclude them on this ground 

 is somewhat dangerous, unless we are pre- 

 pared to admit, off hand, that species are 

 purely artificial. 



It is the custom to speak of bacteria 

 and Saccharomycetes as degenerate forms. 

 What is meant by this expression is not 

 plain, unless it means that, arising presum- 

 ably from plants in which sexuality was 

 present, they have become non-sexual. 

 Undoubtedly sexuality is the rule in nature, 

 but it should be borne in mind that it is 

 not universal. I do not refer here to fungi 

 like Ascomycetes and Basidiomycetes which, 

 accepting the hasty conclusions of the 

 Brefeld school, have been, even by a good 

 many of our own botanists, included in the 

 limbo of non-sexual, degenerate forms from 

 which more recent observers are gi-adually 

 rescuing them. I refer rather to species 

 like Rhodymenia pahnata, one of the com- 

 monest red seaweeds of the North Atlantic, 

 in which, so far, nothing has been discov- 

 ered but the non-sexual tetrasporic repro- 

 duction. This is not an isolated case and 

 others will probably occur to my hearers. 

 Furthermore, we must admit that the num- 

 ber of species normally sexual but in which 

 apogamy sometimes occurs has been percep- 

 tibly increased by the studies of botanists 

 in recent years. In such cases as that of 

 Rhodymenia it may be that the cystocarpic 

 fruit really exists and will be found later, 

 but, since botanists have searched for it in 

 vain for many years, it must be very rare, 

 and certainly, as far as we know it, the plant 

 is non-sexual. 



In regard to cases of apogamy we have 

 not yet sufficient data as to their capacity 



for propagating themselves continually 

 apogamously, although in such cases as 

 that of Chara crinita, if we may judge by the 

 distribution of the species in central Europe, 

 there seems to be no reason to believe that 

 they may not do so indefinitely. The not 

 inconsiderable number of species of mosses, 

 some of them common species, in which the 

 male or female only is known and the num- 

 ber of marine algse which, in spite of their 

 frequency, bear only tetraspores or at most 

 bear cystocarps very rarely, should make 

 us cautious in so defining what we meanby 

 species as to imply that we consider that 

 the perennial succession refers only to suc- 

 cession by sexual generation. 



We cannot fail to notice an increasing 

 tendency among cryptogamic botanists to 

 give more and more weight to physiological 

 characters in limiting their species. For 

 some time we have been accustomed to 

 think of the species of bacteria as largely 

 physiological, and we are gradually accus- 

 toming ourselves to the views of those who 

 hold the same view in regard to species of 

 Saccharomycetes. More recently still we 

 find that in another higher order of fungi, 

 the Uredinace£e, experts are coming more 

 and more to rely on physiological charac- 

 ters. If in bacteria and Saccharomycetes 

 we have plants which are generally recog- 

 nized to be non-sexual, in Uredinacese the 

 probability is that there is sexuality ; at 

 least the probability is here much stronger 

 than in the other two groups. By some the 

 sexuality of Uredinacese is considered al- 

 ready proved, but admitting that the form 

 of nuclear union demonstrated by Dangeard 

 and Sappin-Trouffy and confirmed by some 

 other botanists must have some important 

 significance, not only in this, but in other 

 orders of fungi where it occurs, there are 

 reasons for not regarding the union in this 

 case as representing true sexuality. On 

 the other hand, although no one has yet 

 quite proved it, there appear to be reasons 



