INTRODUCTION. 



between those of the parcuU. We have repeatedly stated 

 that a.i the outcome of growth localization, intercellular 

 (pace* of a hybrid are modified in lize and shape as are 

 the cell* whu-h Mim-und them Now Una clearly demon- 

 strates that the living |>ruto|>la*m which ha* formed the 

 cells ia * 1 m its m -Uvular or micellar < 



i that m il and over every intiuitesimally 



minute are* ou iU surface where cellulose is to be laid 

 duwu the balanced effect of both parent* i* felt. 



i D the laying down of secondary wall thick- 



ening*, whether of a . utu ulanzed, ligmfied, or colloid 

 nature, numerous citation* have been nude where the 

 amount and nunlc of deposition i* evenly between the 

 .:u-.- of the parent*, i'erhaps the mot striking case 

 i* that of the bundle-sheath cells of 1'hilayena and its 

 :.-. where usually five liguified lamella are traceable 

 in each cell of Lapageria, eleven or twelve in /'A I/MM. 

 ^it ir nine in 1'hilageria. 



In Mimman.'.,ng a* to protoplasm and its modifica- 

 tion* a* plastids, where considerable difference* can be 

 tra.xd in the pUutids of two parents the hybrid gives 

 results. Only in a few parent plants have these 

 differences been sufficiently marked to allow of compari- 

 son with the hybrid. The leucoplasts in the epidermal 

 cells of the parents of Dianthtu lindsayi are very differ- 

 ent in sue. while most of the leucoplasts in the hybrid 

 \actly intermediate, but from careful measurement 

 of lantern projection images of these it has been found 

 that .-.-in.' i- try nearly retemble those of the female parent. 

 iMiuopiasts of the petal cells in Gewn intermedium 

 and of the sepal cells in Masdevallia cheUoni are addi- 

 tional illustrations. Those of the former are very varia- 

 ble in size and number, but this is probably to be ex- 

 plained from its inheriting half of its hereditary features 

 from Gtum rivale, which is equally variable as a species. 

 Leaves of corresponding age and position from Saxifraga 

 andreu-sii and its parents have furnished chloroplasts 

 of small size and dark green color in one parent, of large 

 size and soft emerald green color in the other, and an 

 intermediate type in the hybrid, though some diverge 

 towards the " if turn " parent in having large chloroplasts. 



" Hut the average size, shape, and lamellar deposition 

 in starches of Hedyrhium hybrids are perhaps the most 

 interesting cases adduced. When we remember that 

 these are bodies formed temporarily as reserve food, and 

 that they are built up by addition of successive micella 

 through the agency of minute protoplasmic masses or 

 plasts, we have a direct proof that these leucoplasts 

 are themselves fundamentally modified. Their activity 

 in the cells of the hybrid is evinced by the building up of 

 starch grains which, though only of temporary duration 

 in the history of the plant, are so accurately constructed 

 as to be an exact combination in appearance of a half 

 corputcle of each parent. 



" Finally, we may recall the facts advanced as tn 

 color, flowering period, chemical combinations, and 

 grou-th rigor, which, though scanty and fragmentary in 

 their nature, all point to the conclusion that hybrids 

 are intermediate between their parents in general life 

 phenomena." 



In reviewing this summary one is struck by the rec- 

 ords of universality of interme dial f ness by blended or 

 exclusive inheritance of every property. In not a single 



instance is any character developed m either direction be- 

 yond the ritreines of development of the corresponding 

 character of the parents. However, these conclusions 

 are doubtless to be taken as being general or broad rathet 

 than as dogmatic, inasmuch as here and there in the text 

 of the memoir there are records of departures beyond 

 parental extremes, as in Philageria veitchii, in connec- 

 tion with which it is stated it is generally to be noticed 

 that both upper and lower epidermal cells of the hybrid 

 are equal to, if not larger than, the largest of either 

 parent "Those of the one parent (Lapageria rosea) 

 are on an average larger than those of the other parent 

 (Philesia folia), while in the hybrid they may be larger 

 than in either"; also, in the hybrid Bryanthus erectut, 

 in which " the power of conglomerate crystal formation 

 is not only inherited from the male parent (Menziesia 

 tmpetriformu var.) but also appears on a more exag- 

 gerated scale, there being at least 50 per cent more crys- 

 tals in a given area of the hybrid pit than in the 

 parent"; and also, as is quite common, in the greater 

 luxuriance of growth of the hybrid than of the parents, 

 as instanced in Philageria veitchii, Oeum intermedium, 

 Bryanthus erectiu, etc., which peculiarity is attributed 

 by Max-far lane to an increase in the size rather than in- 

 creased multiplication of the cells of the hybrid over the 

 parents; bat in either case it is obvious that there is 

 higher development of the hybrid in relation to the 

 parents ; moreover, even where intermediatoness has been 

 recorded, it has been recognized in some instances that 

 the characters of the hybrid " very nearly resemble those 

 of female parent," etc. In support of Macfarlane, Davis 

 (American Naturalist, 1911, XLV, 193; 1912, XLVI, 377), 

 in studies of the offspring of different species of Oeno- 

 thrra, found that in gross morphological characters the 

 hybrids are intermediate between the parents, and he has 

 since recorded that in histologies! characters they exhibit 

 the same peculiarity. Holden (Science, 1913, xxxnii, 

 932) states that spontaneous hybrids that are recognized 

 as varietal modifications of species can often be diagnosed 

 by their internal anatomy, both vegetative and reproduc- 

 tive, referring particularly to the intermediate histologi- 

 cal characters of the tissues and to abortive pollen. A 

 number of references are given by Holden to the results 

 of the investigations of Be tula and E quite turn, instanc- 

 ing in the hybrid transitional features between the 

 parents in internal and external anatomy associated with 

 abortive spores of hybrids. Reference might be made, 

 did space permit or were it necessary, to various other 

 articles which also are in support of the conception that 

 hybrids are in morphological and anatomical characters, 

 distinguished by " intermediatcness." 



IXTERMEDIATEXES8 OP THE STABCTtU OF HTBBTM. 



Macfarlane (for. cit.) made notes of the starches of 

 Ribet cuhertcellii and its parents, of Bryanlh us erect us 

 and its parents, and of ffedychium hybrids and their 

 parents. He records that in Rib ft grottvlaria (parent) 

 the largest grains are 7/ and the average 4? ; in K. nig- 



