254 



SCIENCE 



[N. S. Vol. XXXIII. No. 842 



DO FERNS HYBRIDIZE? 



In a paper entitled " Physiological Aspects 

 of Fertilization and Hybridization in Ferns,"' 

 Dr. W. D. Hoyt gives considerable space to 

 the evidence heretofore brought forward to 

 prove hybridity among ferns. After consid- 

 ering the evidence under three headings, viz., 

 (o) characters of the mature sporophyte, (&) 

 experiments in which prothallia of different 

 species have been grown together and some of 

 the resulting plants have been considered in- 

 termediate, (c) experiments in which sperms 

 of one species have been presented to eggs of 

 another species, and their behavior watched, 

 he concludes that the affirmative evidence is 

 entirely insufficient, and that the only evidence 

 which is worthy of consideration is negative. 

 He also adduces what he considers additional 

 negative evidence based on his study of the 

 behavior of the gametes of certain ferns with 

 which he worked. 



Dr. Hoyt's paper deserves consideration for 

 its physiological features. His experiments 

 and observations as to the behavior of the 

 sperms and the fusion of the gametes are 

 extremely interesting. Unfortunately, how- 

 ever, the paper does not deserve serious con- 

 sideration with respect to his conclusions re- 

 garding the evidence as classified under the 

 first two headings. His conclusions on these 

 points carry no weight whatever, because they 

 are not based on a first-hand knowledge of the 

 facts concerned. 



For example, in order to be sure of the 

 identity of the common ferns with which he 

 worked, such as Dryopteris Thelypteris, he felt 

 obliged to send his material to Mr. W. E. 

 Maxon for identification. What weight then 

 can his opinion carry with regard to what 

 forms constitute reasonable variations of these 

 common species and what forms are so differ- 

 ent as to deserve a specific if not a hybrid 

 rank? Dr. Hoyt's work with fern hybrids 

 suggests the story which is told of a certain 

 (or rather uncertain) investigator of the 

 embryology of a species of Pinus who did not 

 know the tree in life. Moreover, when Dr. 

 Hoyt was beginning his study of this par- 



"■Bot. Gaa., 49: 340-370, 1910. 



ticular problem at the New York Botanical 

 Garden, he did not even care to examine ample 

 material of nearly all the reputed hybrids of 

 Dryopteris, although he was offered every op- 

 portunity to do this. Apparently his mind 

 was already made up on this point. He 

 wished only to see the experimental plants 

 which Miss Slosson produced by planting in 

 pairs unisexual portions of the prothallia of 

 Dryopteris cristata (L.) Gray and D. margin- 

 alis (L.) Gray, and Asplenium platyneuron 

 (L.) Oakes and Camptosorus rhizophyllus (L.) 

 Link, respectively. The fact that these ex- 

 perimentally produced plants are identical 

 with the wild plants described as the hybrids 

 of these pairs of species. Dr. Hoyt explains 

 easily by suggesting that all may be mere 

 variations. If he had known well the parent 

 species and the reputed hybrids, he could not 

 have made such a suggestion. Either there 

 are hybrids in Dryopteris, et al., or else there 

 are a considerable number of undescribed new 

 species. 



The third class of evidence is the only kind 

 of which Dr. Hoyt has any adequate knowl- 

 edge, and even here his unfamiliarity with 

 the wild plants has reduced to a vanishing 

 point the negative value of that which he 

 presents. Thus he cites as the main evidence 

 which he offers to disprove hybridity among 

 ferns, the fact that he was unable to cause 

 fusion between the gametes of two species 

 which no one has ever suspected from field 

 study to be in the habit of crossing, i. e., 

 Dryopteris Thelypteris (L.) Gray and Dryop- 

 teris novehoracensis (L.) Gray. Sixty-seven 

 attempts he records as having been made to 

 secure the fusion of an egg of one of these 

 with the sperm of the other, but, as he ob- 

 serves, most of the eggs " looked bad," that is, 

 incapable of fertilization, so that his main 

 conclusion rests on a few attempts to cross 

 two species which a knowledge of the wild 

 plants would have warned him not to use. 

 It is to be regretted that he did not try to 

 cross Dryopteris cristata with Dryopteris 

 marginalis. 



He reports four negative attempts to cross 

 Asplenium platyneuron (L.) Oakes with 

 Camptosorus rhizophyllus (L.) Link, between 



