120 BOTANICAL GAZETTE [February 



Now if crypthybrids could justly be called true species, it might 

 possibly be admitted that they to some extent support the muta- 

 tion theory of DeVries. But unfortunately they are frequently, 

 although not universally, very variable, and this variability would 

 appear on morphological grounds to be the result of hybridization. 



On the other hand, the natural hybrid or phenhybrid found in 

 the angiosperms and resulting from a cross between distinct species, 

 with no segregation as in Mendelian crosses, but a blending of the 

 parent characters, may breed true to these respective characters, 

 in which case a new and distinctive form is perpetuated, and to this 

 the systematist may justly give a specific rank. Such forms, how- 

 ever, are usually characterized by a large amount of sterile pollen, 

 unlike the true species in which the pollen is morphologically perfect. 

 Hence the term species is used here in a sense somewhat different 

 from that ordinarily implied. 



In proportion to the extension of the term species, the number 

 of species has grown astonishingly. This multiplication of species 

 is probably largely due to hybridization, judging from the morpho- 

 logical data afforded by the Rosaceae; and generally the new 



a : 99 



species are crypthybrids. Hoar 8 of this laboratory has been 

 investigating Rubus and has reached results corresponding to those 

 recorded here with regard to Rosa. Hybridism appears to be even 

 more rife in Crataegus, and the multiplication of species is likewise 

 greater, as is shown by the result of work carried on by Miss Lora 



Standish. 9 



many of t 

 Arboretum 



and how many are true species and phenhybrids. Take the 3 

 groups as presented according to their pollen sterility. To the 

 first group only can the term species be accurately applied, that is, 

 in the strict sense of the word as used of species of Pinus and 

 Lycopodium; for only in this group is the percentage of sterile 



members may 



some 



8 Hoar, C. S., Sterility as the result of hybridization and the condition of the 

 pollen in Rubus. Bot. Gaz. 62:370-388. 1916. x 



9 Standish, Lora, What is happening to the hawthorns? Jour. Heredity 

 7: 266-279. 1916. 



