IVn;nl>r<TI<»\. 



:;. i m bmediateness a.nh lessened vitality 

 01 Etbkids, etc. 



The gross structural character? of plants have at- 

 i th e attention of mankind from time immemorial, 

 ms they have constituted the essential 

 j which plants have been differentiated and 

 beneath them there lay an infinitude of 

 , chemical, physical, ami physico-chemical 

 rties Hi' tissues and various protoplasmic substances 

 which will undoubti dly be found to he of far greater sig- 

 .., differentiation, not only in taxonomy and 

 . ,, but also in Hi" elucidation of various prob- 

 constantly confront the hotanist. The seien- 

 i of the histological method of plant study to 

 aatisl w&e - it isfactorily demonstrated in 1883 by 

 i m " Uher die Methoden in der botanischen 

 Systematik insbesonderedieanatomische Methode." This 

 method he holds is applicable to the study of species, and 

 since his time it has been successfully extended to varie- 

 ds. A century ago De Candolle found the 

 mien as t'ul in plant classification, and Eadlkofer 



tn| in his memoir that the energies of the systemat- 

 ic would for the next century be devoted to the histo- 

 il method. Previous to the investigations of the 

 ork on the micro-anatomical and the micro- 

 chemical peculiarities of plants was recorded, and since 

 then literature of this character has accumulated to an 

 enormous volume, as is evident at a glance through the 

 pages of Snlereders " Systematische Ana- 

 Dicotyledonen " that appeared in 1898. While 

 miles have proved to be of value in taxonomy, 



in the explanati E many problems that baffled the old- 



ti matist, and in throwing open new avenues of 



lit and investigation, but little has been systema- 



1 that seems to be of immediate practical usefulness 



to the plant-breeder and to the student of evolution. 



Time will undoubtedly show, with the sifting out of these 



records in conjunction with recent work, a wealth of 



iM that far exceeds in value even the greatest 



ctations. 



All of our knowledge of hybrids dates from a period 

 than two centuries ago. ft was near the 

 end of the seventeenth century when the existence of 

 of plant- was recognized, and it was some- 

 time shortly antedating 1710 that Thomas Pairchild, a 

 leneT, produced a hybrid (Fairchild Sweet 

 William) by the fertilization of Dianthus caryophyllus 

 ink) with D. barbatus (the common Sweet 

 am). This was followed by investigations of 

 and hybrids by Linnaeus. To Kolreuter, how- 

 iments in hybridization began 

 in L760 by crossin i rustica with N. panicw- 



lata, must be given the credit for laying a working foun- 

 dation that has proved of the greatesl value in arousing 

 active investigation in this exceptionally 

 i field o h. What had been recorded 



of both naturallv and artificially produced hybrids up 



to 35 years ago was summarized and commented upon 

 by Focke (Die Pflanzen-MiscbJ B 



der Gewachse, L881). Probably as many as 2,000 

 hybrids are here referred to. Since then the number has 

 been considerably added to in botanical literature. Such 

 investigations, up to the time of the appearance of the 



memoir by Macfarlai □ " A Comparison of the Minute 



Structure of Plant Hybrids with that of their Parents 

 and its Bearing on Biological Problems" thai appeared 

 in 1892, were confined practically wholly to the grosser 

 phenomena of plant life, such as the parentage, size, 

 vigor, rapidity of growth, length of life, appearance of 

 malformations, fertility, etc. — in a word, gross charac- 

 ters such as have been and continue to be the tools of 

 the old-school systematist. 



Intekmediateness of Histologic Properties 

 of Hybrids. 



Macfarlane in referring to the earlier microscopical 

 investigations states that Henslow (Cambridge Phil. 

 Trans., 1831) made a microscopic comparison of a hybrid 

 Digitalis with its parents and showed that in the size 

 and shape of the hairs and other structures the hybrid is 

 intermediate between the parents; that Wichura (Bas- 

 tardefruchtung, 1865) with Snli.r, and Kernel ( Mono- 

 graphia Pulmonar., 1878) with Pvlmonaria, likewise 

 found the hybrid to be intermediate; and that Wettstein 

 (Sitz. der. Kaiser. Akad. der Wissen., 1888), in compar- 

 ing the leaves of four coniferous hybrids observed in 

 transverse sections of the leaves that each hybrid in the 

 number of stomata, depth of the epidermal cells, and 

 number and arrangement, of the sclerenehyma elements 

 of the bundles is exactly intermediate between their 

 parents. 



In investigations of the minute characters of over 60 

 hybrids in comparison with their parents, Macfarlane 

 found it necessary to adopt certain precautionary meas- 

 ures in order to secure safe comparative results. Inas- 

 much as they have served as our guide in the anatom 

 part of the present rc=careh they are here quoted in fell: 



1. Average Organismat. Development am Deviations. 



"' It is now recognized by botanists that every species 

 exhibits a sum-total of naked-eye characters which dis- 

 tinguish it with greater or less precision from allied 

 species. These are duly given in every local Flora. 

 But further, specific features— alike macroscopic and 

 microscopic- which are of great importance, are passed 

 over. Radlkofer (Akad. der Wissenschaften, Munich, 

 L883) has already insisted that the anatomical method 

 must he applied 'to the study of species, and 1 have 

 n .niited out that this is equally true of Bubspecies anil 

 varieties (Trans. Bot. Sue. Edin., vol. XIX, 1891). Hut 

 it is the sum-total or accumulation of minute peculiari- 

 bies which gives specific identity to any or nanism, and it 



is to 1 xpected that evident or naked-eve variations 



will often have their commencement in trivial structural 

 deviations, which, being perpetuated and exaggerated 

 it may be in size, will ultimately appeal to the naked 



