24 



Transactions. 



growth-forms. Although the juvenile and adult forms may be so dis- 

 tinct as to virtually represent different species, yet in many cases the adult 

 does not appear suddenly, but intermediate stages occur. In these there 

 is very frequently a combination of characters which are primarily quite 

 distinct. Thus in the intermediate leaf-form of Parsonsia capsularis E. Br. 

 (see fig. 2) there are all kinds of combinations between the early seedling 

 short rounded leaf and the later long narrow one. Elaeocarpus Hookerianus 

 Raoul also exhibits a remarkable series of leaf-combinations, for which 

 see fig. 3. Further, there are transitions of general growth-forms, as when 

 Sophora microphylla Ait. commences the adult stage with stout semi-erect 

 but still flexuous stems. It seems clear from the above facts and from 

 those that follow that the possibilities of both juvenile and adult are 

 latent in the one plant, but each requires its necessary stimulus to set it 

 free in its entirety. If the stimulus is not sufficient, then one or the other 



t VP» f 



\ 



Fig. 2. — Various Forms op Leaf in Parsonsia heterophylla. 



a, adult leaf ; / and g, earliest form of leaf, but often more circular ; d, e, and h, tran- 

 sitional forms ; b and c, second type of juvenile leaf. Life size. 



form may persist, or there may be a combination of characters, as in the 

 transitional forms. In any case, heredity comes in, and this has attained 

 to such a degree that under normal conditions there is a juvenile stage of a 

 certain average duration, a transitional stage, and an adult. Different 

 degrees of heredity have arisen, as I believe, in proportion to the length 

 of time the original stimuli have functioned, combined with their intensity, 

 and abnormal increase or decrease of stimulus can in many instances 

 hasten or retard the procession of events. There is in some measure, per- 

 haps, species-making going on before our eyes. This is best seen in those 

 cases where the juvenile form produces flowers, for if progressive develop- 

 ment should cease at this point what is virtually a species distinct from 



