10 



INTRODUCTION. 



tion of compoundness, inasmuch as some of the round 

 grains are compound and some single; (c) it is inter- 

 mediate in the degree of compoundness, inasmuch as 

 amongst those round grains which are compound the 

 most common number of constituent pieces is 3, whereas 

 in compound grains it is 6. 



2. In a subsequent generation (F 6 ) the homozygote 

 round peas contain potato-shaped grains and the hetero- 

 zygote round peas contain round or intermediate grains. 

 But both round and intermediate grains may be asso- 

 ciated either with a high or a low degree of compoundness. 



3. Potato-shaped grains occasionally occur in 

 wrinkled peas in F B , and the evidence suggests that the 

 existence of these grains in wrinkled peas tends to make 

 them less wrinkled. 



4. A wrinkled pea takes up more water when it ger- 

 minates than a round one. The hybrid between a round 

 and a wrinkled pea is intermediate in respect to this 

 character between its two parents. 



5. But the intermediateness of the hybrid in absorp- 

 tion capacity is not occasioned by the intermediateness 

 of the starch-grain of the hybrid, because both F 2 peas 

 containing round grains and peas containing potato- 

 shaped grains have the same absorption capacity as the 

 F, pea. 



6. When, therefore, a round pea is crossed with a 

 wrinkled pea, four separately heritable characters are 

 dealt with : (a) the shape of the pea, whether round 

 or wrinkled; (b) the absorption capacity of the pea as 

 regards water, whether low or high; (c) the shape of the 

 starch-grain, whether long or round; (d) the constitution 

 of the starch-grain, whether single or compound. 



The results of these researches are not only confirma- 

 tory of the records of Macfarlane in showing interme- 

 diateness in the microscopical properties of the starch of 

 the hybrid, but also go further by demonstrating other 

 forms of intermediateness. 



INTERMEDIATENESS OF THE MACROSCOPIC PROPERTIES 

 OF HYBRIDS. 



No criterion of hybrids is more widely recognized 

 than intermediateness of naked-eye characters. Refer- 

 ences have been made incidentally in preceding sections to 

 these peculiarities, but inasmuch as macroscopic charac- 

 ters have been the essential tools of the systematist 

 it is here that we must look for the data that constitute 

 the great foundation stones upon which rests the doctrine 

 of intermediateness. Macfarlane in summarizing the 

 gross characters of parent-stocks and hybrids states that 

 " color, flowering period, chemical combinations, and 

 growth-vigor, which, though scanty and fragmentary in 

 their nature, they all point to the conclusion that hybrids 

 are intermediate between their parents in general life 

 phenomena." Masters (quoted by Macfarlane, ibid., 

 page 209) in comparing the bigeneric hybrid Philageria 

 veitchii with its parents Lapageria rosea and Philesia 

 buxifolia states : 



"In habit our plant [the hybrid] is, of the two, 

 more akin to the female parent (Lapageria) than to the 

 male. Its foliage is singularly intermediate, but at the 

 same time nearest like that of the pollen parent (Phi- 



lesia). In the characters of the flower-stalk, calyx, and 

 corolla, it is more like Philesia than Lapageria, but in 

 the stamens it approximates to the mother-plant, and 

 diverges from the characters of the male. In color it is 

 also more like the mother-plant than it is like Philesia. 

 The fruit we have not seen. The characteristics of both 

 parents are so curiously blended that we fear this plant 

 will lend much aid to those investigators who are striving 

 to determine what is the effect on the offspring of pollen 

 or seed parent, respectively. On the whole, it would 

 seem as though the organs of vegetation, including the 

 calyx and corolla, were more like those of the male 

 (Philesia), while in the stamens and pistil the progeny 

 favor the mother." 



From the foregoing data in this and preceding sec- 

 tions one is led to the belief that intermediate inheritance 

 in the first generation is almost so universal as to be all 

 but a law, but such a conception is inconsistent with a 

 considerable mass of literature pertaining to both plants 

 and animals. Focke (loc. cit.), in his Fourth Lecture, 

 summarizes under five propositions a most important col- 

 lection of data pertaining to the characters of hundreds 

 of hybrids and their offspring. Inasmuch as these facts 

 are of great interest, fundamental importance, and broad 

 applicability, and as scant recognition seems to be given 

 to this work, and as the book is rarely found in our librar- 

 ies, a translation of his lecture is here given practically 

 in full : 



PROPOSITIONS OF FOCKE. 

 FIBST PROPOSITION. SIMPLE PRIMARY HYBRIDS (AxB). 



If individuals which have sprung collectively from the crossing 

 of two pure species of races are produced and groim under 

 similar conditions they resemble one another exactly, or 

 are, as a rule, hardly to lie differentiated, from one another 

 just as in specimens belonging to one and the same species. 



The principle thus formulated seems in many ex- 

 periments to be sufficiently well-grounded, but it has 

 many exceptions. Several instances in hybrids indicate 

 such similarity only of individuals produced from the 

 same impregnated part (seed pod, etc.). In any event, 

 the rule proves trustworthy only in cases in which simi- 

 larity of conditions of production and growth are 

 present. 



It is difficult to answer satisfactorily a most stren- 

 uously debated question if one or the other sex has the 

 stronger influence on the form of the offspring. The 

 hybrids of the two species or races, A and B, are like 

 one another no matter whether A in the crossing was the 

 male or the female progenitor. Kolreuter, Gartner, 

 Naudin, and Wichura in common could find no differ- 

 ences between the products of the two crossings A 9 X 

 B d" and B ? X A j More than 100 years after Kol- 

 reuter noticed the similarity between the crosses Nico- 

 tiana rustica 9 X N. pardculata, c? and N. paniculata 

 9 X N. rustica $ , and one of the most observant botan- 

 ists of our time, Timbal-Lagrave, was astonished by a 

 similar experience. All the rules and assumed prin- 

 ciples by which botanists try to determine by the mor- 

 phological characteristics of the hybrid which is the pol- 

 len and which is the seed parent prove to be entirely 

 theoretical and of no value. It has been established by 

 many experiments that in the case of pure species in the 



