•278 DR J. M. MACFARLANE ON THE 



urged against it. The fundamental idea animating the pangenetic theory is that the sex- 

 eells are the cumulative expression of all the actions and reactions, the integrations and 

 disintegrations which have been associated with the protoplasms up to the time when 

 these sex-cells have been fully formed. Nageli in expressing the same fundamental idea 

 brought it more into line with modern cell discovery by assuming that the nucleoplasm 

 was a continuous network. Weismann has objected to Nageli's hypothesis * as follows : — 

 " The idioplasm does not form a directly continuous network throughout the entire 

 body," and " it is perfectly certain that the idioplasm cannot form a continuous network 

 throughout the whole organism if it is seated in the nucleus and not in the cell-body." 



But it may well be asked, How do we know that idioplasm, nuclear substance, nucleolar 

 substance, or chromatic substance, is not connected into one network ? A dozen years 

 have not passed since the majority of biologists would have rejected the idea of an 

 intercellular network. Our minds should be open to receive fairly any hypothesis, 

 or facts favouring a hypothesis, that may be presented without dogmatising that such 

 cannot be. 



We repeat it, then, as an observed fact, that the reproductive cells of hybrids are to a 

 greater or less extent small, imperfect, and badly formed, and that the more divergent 

 the parent types the more numerous do the imperfect cells become. If with Weismann 

 we view each of these as descendants from the germ-plasm of the hybrid egg, why do 

 these fail to mature and continue the hybrid progeny ? It may be replied that the 

 susceptible germ-plasms refuse to blend, or blend so imperfectly, that while the blended 

 somatoplasms develop the vegetative part of the. hybrid, the germ-plasms break down. 

 But this compels us to assume a greatly more cumbrous state of matters than does the 

 pangenesis theory, for we must suppose that these imperfectly blended masses of germ- 

 plasms are carried up with the growth of the stem, and finally appear at the floral 

 extremities in an aborted state, and that this continues year after year in a hybrid shrub 

 or tree ; and we must further assume in the case of Cytisus Adami, that the same is 

 effected by vegetative union of the parts of two parents, without the intervention of 

 sex-cells. It may be urged in the latter case that some germ-plasm cells were mixed up 

 amongst the apparently pure vegetative or somatoplasmic cells, but even if this be 

 granted, it still proves that a hybrid growth can develop apart from sexual union. We 

 believe that a simple and more natural explanation can be given, a short summary of 

 which has already appeared in Nature(vol. 44, 1891). 



(g) Vegetable Cell Structure in Relation to Hybridity. — Observations made by me, 

 alike on resting and dividing cells, during the last few years, and preparations which Mi- 

 Mann made and kindly showed me, caused me to adhere to my already published views on 

 cell-life, viz., that in the ordinary resting state of an active cell, i.e., one capable of, and 

 at times showing, division, a nucleus with nucleolus and endo-nucleolus are integral parts, 

 and that after division of the cell has ceased proliferation of the inner parts may still go on 

 leading to a multi-endonucleolar, then to a multi-nucleolar, and finally to a multi-nuclear 



* Biological Memoirs, first English ed., pp. 180, 181. 



