78 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



the probability of germ-plasm being always associated with protoplasm 

 would seem to form a necessary part of the theory. 



But, then, the converse becomes at once more probably true, viz. that 

 there is no such substance at all as germ-plasm, the protoplasm itself 

 being quite able to do all the work that is required. 



Microscopic investigations of the germ-cells, which give rise to 

 embryos, exhibit definite structures called " chromosomes," which enter 

 into the first cell of the offspring, and as there must be something to carry 

 on hereditary tendencies, these are most probably the agents ; but their 

 chemical constitution is unknown. 



Dr. Weismann contends that if the deep-seated germ-plasm could be 

 influenced by external agencies, then their effects might be retained and 

 hereditary ; but as a rule the soma intervenes and would prevent any such 

 influences from affecting the germ-plasm, the existence of which, however, 

 has never been optically proved. 



The question, then, which Weismann and his followers give to be 

 answered is : Can any change of form and structure induced by external 

 causes in the soma of a plant be transmitted to the next generation 

 irrespective of conditions ? 



The only reply is to see what nature does, and to test it by experi- 

 ments. These supply two lines of proof, inductive evidence and experi- 

 mental verification. 



It has long been noticed that the floras of countries with pronounced 

 climatal conditions are characterised by having a more or less general or 

 common fades. Hence we are familiar with the terms arctic and alpine 

 plants, remarkable, for example, by their dwarf character and the brilliant 

 colours of many of the flowers. Then there are moist tropical floras, hot 

 desert plants, and so on. 



Now all the plants growing under such several conditions reproduce 

 the features characteristic of the genus, species, &c, by seed ; so that 

 they are obviously hereditary, as long as they live under the same con- 

 ditions. 



Do they change if taken away from their natural surroundings and 

 are, say, cultivated ? As a rule they do not at first show, to any great 

 extent, any alteration in strongly marked features. Thus seedling 

 Opuntias, Cactuses, &c, retain their characters if raised artificially. 



On the other hand, many plants begin to change at once. Thus 

 naturally hairy plants may become hairless, fleshy maritime plants may 

 acquire ordinary thin leaves away from the coast. 



Similarly, aquatic plants if crowded will often thrust up branches into 

 the air, the anatomy of which at once changes at the water-level in 

 adaptation to an aerial existence. 



The next question is, what are the causes which give rise to any 

 peculiar fades ? Why are so many plants fleshy in dry countries, like the 

 Cactacece of Mexico and the Euphorbias, Stapelias, and Mesembryanthe- 

 mums of South Africa ? 



Or, on the other hand, why have so many dicotyledonous plants 

 finely dissected leaf-blades when growing under water ? Is it drought in 

 the first case, and water in the second case, that are the causes ? 



Inductive evidence means that there exists a vast accumulation of 



